import java.util.*;
import java.io.*;

public class Main {

    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main {

    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} Main public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    } main {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    } try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{} catch(Exception e){e.printStackTrace();} Exception e {e.printStackTrace();} e.printStackTrace() e.printStackTrace e {} {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        } Reader fr = new Reader(); fr new Reader() OutputStream out = new BufferedOutputStream(System.out); out new BufferedOutputStream(System.out) long a = fr.nextLong(); a fr.nextLong() fr.nextLong fr long b = fr.nextLong(); b fr.nextLong() fr.nextLong fr long c = fr.nextLong(); c fr.nextLong() fr.nextLong fr long d = fr.nextLong(); d fr.nextLong() fr.nextLong fr List<Long> list = new ArrayList<>(); list new ArrayList<>() long ans1 = a*c; ans1 a*c a c long ans2 = a*d; ans2 a*d a d long ans3 = b*c; ans3 b*c b c long ans4 = b*d; ans4 b*d b d long ans5 = c*a; ans5 c*a c a long ans6 = c*b; ans6 c*b c b long ans7 = d*a; ans7 d*a d a long ans8 = d*b; ans8 d*b d b list.add(ans1) list.add list ans1 list.add(ans2) list.add list ans2 list.add(ans3) list.add list ans3 list.add(ans4) list.add list ans4 list.add(ans5) list.add list ans5 list.add(ans6) list.add list ans6 list.add(ans7) list.add list ans7 list.add(ans8) list.add list ans8 long ans = Collections.max(list); ans Collections.max(list) Collections.max Collections list out.write((ans+"\n").getBytes()) out.write out (ans+"\n").getBytes() (ans+"\n").getBytes (ans+"\n") ans "\n" out.flush() out.flush out out.close() out.close out String[] args args static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    } FastReader BufferedReader br; br StringTokenizer st; st public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        } FastReader {
            br = new BufferedReader(new InputStreamReader(System.in));
        } br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } next {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        } while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            } st==null || !st.hasMoreElements() st==null st null !st.hasMoreElements() st.hasMoreElements() st.hasMoreElements st {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            } try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                } catch(IOException e)
                {
                    e.printStackTrace();
                } IOException e {
                    e.printStackTrace();
                } e.printStackTrace() e.printStackTrace e {
                    st = new StringTokenizer(br.readLine());
                } st = new StringTokenizer(br.readLine()) st new StringTokenizer(br.readLine()) return st.nextToken(); st.nextToken() st.nextToken st int nextInt()
        {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        } nextLine {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        } String str = ""; str "" try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            } catch(IOException e)
            {
                e.printStackTrace();
            } IOException e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                str = br.readLine();
            } str = br.readLine() str br.readLine() br.readLine br return str; str static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    } Reader final private int BUFFER_SIZE = 1 << 16; BUFFER_SIZE 1 << 16 1 16 private DataInputStream din; din private byte[] buffer; buffer private int bufferPointer bufferPointer bytesRead; bytesRead public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } Reader {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } din = new DataInputStream(System.in) din new DataInputStream(System.in) buffer = new byte[BUFFER_SIZE] buffer new byte[BUFFER_SIZE] BUFFER_SIZE bufferPointer = bytesRead = 0 bufferPointer bytesRead = 0 bytesRead 0 public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } Reader {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        } din = new DataInputStream(new FileInputStream(file_name)) din new DataInputStream(new FileInputStream(file_name)) buffer = new byte[BUFFER_SIZE] buffer new byte[BUFFER_SIZE] BUFFER_SIZE bufferPointer = bytesRead = 0 bufferPointer bytesRead = 0 bytesRead 0 String file_name file_name public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        } readLine {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        } byte[] buf = new byte[64]; buf new byte[64] 64 int cnt = 0 cnt 0 c; c while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            } (c = read()) != -1 (c = read()) c read() read -1 1 {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            } if (c == '\n')
                    break; c == '\n' c '\n' break; buf[cnt++] = (byte) c buf[cnt++] buf cnt++ cnt (byte) c return new String(buf, 0, cnt); new String(buf, 0, cnt) public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        } nextInt {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        } int ret = 0; ret 0 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        } nextLong {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        } long ret = 0; ret 0 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        } nextDouble {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        } double ret = 0 ret 0 div = 1; div 1 byte c = read(); c read() read while (c <= ' ')
                c = read(); c <= ' ' c ' ' c = read() c read() read boolean neg = (c == '-'); neg (c == '-') c '-' if (neg)
                c = read(); neg c = read() c read() read do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9'); (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                ret = ret * 10 + c - '0';
            } ret = ret * 10 + c - '0' ret ret * 10 + c - '0' ret * 10 + c ret * 10 ret 10 c '0' if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            } c == '.' c '.' {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            } while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                } (c = read()) >= '0' && c <= '9' (c = read()) >= '0' (c = read()) c read() read '0' c <= '9' c '9' {
                    ret += (c - '0') / (div *= 10);
                } ret += (c - '0') / (div *= 10) ret (c - '0') / (div *= 10) (c - '0') c '0' (div *= 10) div 10 if (neg)
                return -ret; neg return -ret; -ret ret return ret; ret private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        } fillBuffer {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        } bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE) bytesRead din.read(buffer, bufferPointer = 0, BUFFER_SIZE) din.read din buffer bufferPointer = 0 bufferPointer 0 BUFFER_SIZE if (bytesRead == -1)
                buffer[0] = -1; bytesRead == -1 bytesRead -1 1 buffer[0] = -1 buffer[0] buffer 0 -1 1 private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        } read {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        } if (bufferPointer == bytesRead)
                fillBuffer(); bufferPointer == bytesRead bufferPointer bytesRead fillBuffer() fillBuffer return buffer[bufferPointer++]; buffer[bufferPointer++] buffer bufferPointer++ bufferPointer public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        } close {
            if (din == null)
                return;
            din.close();
        } if (din == null)
                return; din == null din null return; din.close() din.close din public class Main {

    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} public class Main {

    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
} Main
import java.util.*;
import java.io.*;

public class Main {

    static class FastReader
    {
        BufferedReader br;
        StringTokenizer st;

        public FastReader()
        {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next()
        {
            while(st==null || !st.hasMoreElements())
            {
                try
                {
                    st = new StringTokenizer(br.readLine());
                }
                catch(IOException e)
                {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt()
        {
            return Integer.parseInt(next());
        }

        String nextLine()
        {
            String str = "";

            try
            {
                str = br.readLine();
            }
            catch(IOException e)
            {
                e.printStackTrace();
            }
            return str;
        }
    }

    static class Reader
    {
        final private int BUFFER_SIZE = 1 << 16;
        private DataInputStream din;
        private byte[] buffer;
        private int bufferPointer, bytesRead;

        public Reader()
        {
            din = new DataInputStream(System.in);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public Reader(String file_name) throws IOException
        {
            din = new DataInputStream(new FileInputStream(file_name));
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public String readLine() throws IOException
        {
            byte[] buf = new byte[64]; // line length
            int cnt = 0, c;
            while ((c = read()) != -1)
            {
                if (c == '\n')
                    break;
                buf[cnt++] = (byte) c;
            }
            return new String(buf, 0, cnt);
        }

        public int nextInt() throws IOException
        {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do
            {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        public long nextLong() throws IOException
        {
            long ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');
            if (neg)
                return -ret;
            return ret;
        }

        public double nextDouble() throws IOException
        {
            double ret = 0, div = 1;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();

            do {
                ret = ret * 10 + c - '0';
            }
            while ((c = read()) >= '0' && c <= '9');

            if (c == '.')
            {
                while ((c = read()) >= '0' && c <= '9')
                {
                    ret += (c - '0') / (div *= 10);
                }
            }

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() throws IOException
        {
            bytesRead = din.read(buffer, bufferPointer = 0, BUFFER_SIZE);
            if (bytesRead == -1)
                buffer[0] = -1;
        }

        private byte read() throws IOException
        {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

        public void close() throws IOException
        {
            if (din == null)
                return;
            din.close();
        }
    }

    public static void main(String[] args) throws java.lang.Exception
    {
        try
        {
            //FastReader fr = new FastReader();
            Reader fr = new Reader();
            OutputStream out = new BufferedOutputStream(System.out);

           long a = fr.nextLong();
           long b = fr.nextLong();
           long c = fr.nextLong();
           long d = fr.nextLong();

           List<Long> list = new ArrayList<>();

           long ans1 = a*c;
           long ans2 = a*d;
           long ans3 = b*c;
           long ans4 = b*d;
           long ans5 = c*a;
           long ans6 = c*b;
           long ans7 = d*a;
           long ans8 = d*b;

           list.add(ans1);
           list.add(ans2);
            list.add(ans3);
            list.add(ans4);
            list.add(ans5);
            list.add(ans6);
            list.add(ans7);
            list.add(ans8);

            long ans = Collections.max(list);

            out.write((ans+"\n").getBytes());


            out.flush();
            out.close();
        }

        catch(Exception e){e.printStackTrace();}
        finally{}
    }
}
