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

public class Main {
    public static MyScanner scan;
    public static PrintWriter out;
    public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    }



    //scanner
    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} import java.io.*; io.* java import java.util.*; util.* java import java.lang.*; lang.* java public class Main {
    public static MyScanner scan;
    public static PrintWriter out;
    public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    }



    //scanner
    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} Main public static MyScanner scan; scan public static PrintWriter out; out public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    } main {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    } scan=new MyScanner() scan new MyScanner() out=new PrintWriter(new BufferedOutputStream(System.out)) out new PrintWriter(new BufferedOutputStream(System.out)) int t=1; t 1 while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        } t-->0 t-- t 0 {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        } long[] a=new long[4]; a new long[4] 4 for(int c=0;c<4;c++) a[c]=scan.nextLong(); int c=0; int c=0; c 0 c<4 c 4 c++ c++ c a[c]=scan.nextLong(); a[c]=scan.nextLong() a[c] a c scan.nextLong() scan.nextLong scan out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3])))) out.println out Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))) Math.max Math a[0]*a[3] a[0] a 0 a[3] a 3 Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3])) Math.max Math a[0]*a[2] a[0] a 0 a[2] a 2 Math.max(a[1]*a[2],a[1]*a[3]) Math.max Math a[1]*a[2] a[1] a 1 a[2] a 2 a[1]*a[3] a[1] a 1 a[3] a 3 out.close() out.close out String[] args args public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    } MyScanner BufferedReader br; br StringTokenizer st; st public MyScanner() {
            br = new BufferedReader(new InputStreamReader(System.in));
        } MyScanner {
            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 long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double 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 public class Main {
    public static MyScanner scan;
    public static PrintWriter out;
    public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    }



    //scanner
    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} public class Main {
    public static MyScanner scan;
    public static PrintWriter out;
    public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    }



    //scanner
    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
} Main
import java.io.*;
import java.util.*;
import java.lang.*;

public class Main {
    public static MyScanner scan;
    public static PrintWriter out;
    public static void main(String[] args) {
        scan=new MyScanner();
        out=new PrintWriter(new BufferedOutputStream(System.out));

        int t=1;
//        int t=scan.nextInt();
        while(t-->0) {

            long[] a=new long[4];
            for(int c=0;c<4;c++) a[c]=scan.nextLong();
            out.println(Math.max(a[0]*a[3],Math.max(a[0]*a[2],Math.max(a[1]*a[2],a[1]*a[3]))));

        }
        out.close();
    }



    //scanner
    public static class MyScanner {
        BufferedReader br;
        StringTokenizer st;

        public MyScanner() {
            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());
        }

        long nextLong() {
            return Long.parseLong(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

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