import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;


public class Main {
    final static long MOD = 1000000007;

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    }

    class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    }

    public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    }

    public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    }


    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    }

}

/*class Pair implements Comparable<Pair> {

    int V;
    int H;

    public Pair(int count, int val) {
        this.V = count;
        this.H = val;
    }

    public void setV(int v) {
        V = v;
    }

    public void setH(int h) {
        H = h;
    }

    @Override
    public int compareTo(Pair o) {
         if(this.V != o.V)
            return Integer.compare(this.V, o.V);
         else
             return Integer.compare(this.H, o.H);
    }

    public boolean equals(Pair o) {
        return this.H == o.H && this.V == o.V;
    }
}*/

class Pair {

    int V;
    int H;

    public Pair(int x, int y) {
        this.V = x;
        this.H = y;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Pair)) return false;
        Pair key = (Pair) o;
        return V == key.V && H == key.H;
    }

    @Override
    public int hashCode() {
        int result = V;
        result = 31 * result + H;
        return result;
    }

}
 import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.io.PrintWriter; PrintWriter java.io import java.util.*; util.* java public class Main {
    final static long MOD = 1000000007;

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    }

    class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    }

    public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    }

    public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    }


    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    }

} Main final static long MOD = 1000000007; MOD 1000000007 public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    } main {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    } FastScanner fs = new FastScanner(); fs new FastScanner() PrintWriter out = new PrintWriter(System.out); out new PrintWriter(System.out) long a = fs.nextInt(); a fs.nextInt() fs.nextInt fs long b = fs.nextInt(); b fs.nextInt() fs.nextInt fs long c = fs.nextInt(); c fs.nextInt() fs.nextInt fs long d = fs.nextInt(); d fs.nextInt() fs.nextInt fs out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d)) out.println out Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d) Math.max Math Math.max(Math.max(a* c, a * d), b * c) Math.max Math Math.max(a* c, a * d) Math.max Math a* c a c a * d a d b * c b c b * d b d out.flush() out.flush out out.close() out.close out String[] args args public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    } rString {
        return new StringBuilder(s).reverse().toString();
    } return new StringBuilder(s).reverse().toString(); new StringBuilder(s).reverse().toString() new StringBuilder(s).reverse().toString new StringBuilder(s).reverse() new StringBuilder(s).reverse new StringBuilder(s) String s s public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    } powoftwo {
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    } int count = 0; count 0 while(n != 0) {
            n >>= 1;
            count++;
        } n != 0 n 0 {
            n >>= 1;
            count++;
        } n >>= 1 n 1 count++ count return count - 1; count - 1 count 1 long n n public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    } rotate {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    } int n = nums.length; n nums.length nums nums.length if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        } k > 0 k 0 {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        } for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            } int j = 0; int j = 0; j 0 j < k j k j++ j++ j {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            } {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            } for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                } {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                } int temp = nums[(i + k) % n]; temp nums[(i + k) % n] nums (i + k) % n (i + k) i k n nums[(i + k) % n] = nums[i] nums[(i + k) % n] nums (i + k) % n (i + k) i k n nums[i] nums i nums[i] = temp nums[i] nums i temp int[] nums nums int k k class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    } Pair int index; index int val; val Pair(int index, int val) {
            this.val = val;
            this.index = index;
        } Pair {
            this.val = val;
            this.index = index;
        } this.val = val this.val this this.val val this.index = index this.index this this.index index int index index int val val static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    } FastScanner BufferedReader br; br StringTokenizer st; st public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        } FastScanner {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        } try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            } Exception e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } br = new BufferedReader(new InputStreamReader(System.in)) br new BufferedReader(new InputStreamReader(System.in)) st = new StringTokenizer("") st new StringTokenizer("") public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        } next {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        } if (st.hasMoreTokens())
                return st.nextToken(); st.hasMoreTokens() st.hasMoreTokens st return st.nextToken(); st.nextToken() st.nextToken st try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            } Exception 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 public int nextInt() {
            return Integer.parseInt(next());
        } nextInt {
            return Integer.parseInt(next());
        } return Integer.parseInt(next()); Integer.parseInt(next()) Integer.parseInt Integer next() next public long nextLong() {
            return Long.parseLong(next());
        } nextLong {
            return Long.parseLong(next());
        } return Long.parseLong(next()); Long.parseLong(next()) Long.parseLong Long next() next public double nextDouble() {
            return Double.parseDouble(next());
        } nextDouble {
            return Double.parseDouble(next());
        } return Double.parseDouble(next()); Double.parseDouble(next()) Double.parseDouble Double next() next public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        } nextLine {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        } String line = ""; line "" try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            } catch (Exception e) {
                e.printStackTrace();
            } Exception e {
                e.printStackTrace();
            } e.printStackTrace() e.printStackTrace e {
                line = br.readLine();
            } line = br.readLine() line br.readLine() br.readLine br return line; line public char nextChar() {
            return next().charAt(0);
        } nextChar {
            return next().charAt(0);
        } return next().charAt(0); next().charAt(0) next().charAt next() next 0 public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } nextIntegerArray {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } Integer[] a = new Integer[n]; a new Integer[n] n for (int i = 0; i < n; i++)
                a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } nextIntArray {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        } int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++)
                a[i] = nextInt(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextInt(); a[i] = nextInt() a[i] a i nextInt() nextInt return a; a int n n public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } nextLongArray {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        } long[] a = new long[n]; a new long[n] n for (int i = 0; i < n; i++)
                a[i] = nextLong(); int i = 0; int i = 0; i 0 i < n i n i++ i++ i a[i] = nextLong(); a[i] = nextLong() a[i] a i nextLong() nextLong return a; a int n n public char[] nextCharArray() {
            return nextLine().toCharArray();
        } nextCharArray {
            return nextLine().toCharArray();
        } return nextLine().toCharArray(); nextLine().toCharArray() nextLine().toCharArray nextLine() nextLine class Pair {

    int V;
    int H;

    public Pair(int x, int y) {
        this.V = x;
        this.H = y;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Pair)) return false;
        Pair key = (Pair) o;
        return V == key.V && H == key.H;
    }

    @Override
    public int hashCode() {
        int result = V;
        result = 31 * result + H;
        return result;
    }

} Pair int V; V int H; H public Pair(int x, int y) {
        this.V = x;
        this.H = y;
    } Pair {
        this.V = x;
        this.H = y;
    } this.V = x this.V this this.V x this.H = y this.H this this.H y int x x int y y @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Pair)) return false;
        Pair key = (Pair) o;
        return V == key.V && H == key.H;
    } equals {
        if (this == o) return true;
        if (!(o instanceof Pair)) return false;
        Pair key = (Pair) o;
        return V == key.V && H == key.H;
    } if (this == o) return true; this == o this o return true; true if (!(o instanceof Pair)) return false; !(o instanceof Pair) (o instanceof Pair) o Pair return false; false Pair key = (Pair) o; key (Pair) o return V == key.V && H == key.H; V == key.V && H == key.H V == key.V V key.V key key.V H == key.H H key.H key key.H Object o o @Override
    public int hashCode() {
        int result = V;
        result = 31 * result + H;
        return result;
    } hashCode {
        int result = V;
        result = 31 * result + H;
        return result;
    } int result = V; result V result = 31 * result + H result 31 * result + H 31 * result 31 result H return result; result public class Main {
    final static long MOD = 1000000007;

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    }

    class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    }

    public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    }

    public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    }


    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    }

} public class Main {
    final static long MOD = 1000000007;

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    }

    class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    }

    public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    }

    public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    }


    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    }

} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;


public class Main {
    final static long MOD = 1000000007;

    public static void main(String[] args) {
        FastScanner fs = new FastScanner();
        PrintWriter out = new PrintWriter(System.out);

        long a = fs.nextInt();
        long b = fs.nextInt();
        long c = fs.nextInt();
        long d = fs.nextInt();

        out.println(Math.max(Math.max(Math.max(a* c, a * d), b * c), b * d));
        
        out.flush();
        out.close();
    }

    class Pair{
        int index;
        int val;

        Pair(int index, int val) {
            this.val = val;
            this.index = index;
        }
    }

    public static String rString(String s) {
        return new StringBuilder(s).reverse().toString();
    }

    public static int powoftwo(long n){
        int count = 0;
        while(n != 0) {
            n >>= 1;
            count++;
        }
        return count - 1;
    }

    public static void rotate(int[] nums, int k) {
        int n = nums.length;
        if(k > 0) {
            for(int j = 0; j < k; j++) {
                for (int i = 0; i < n; i++) {
                    int temp = nums[(i + k) % n];
                    nums[(i + k) % n] = nums[i];
                    nums[i] = temp;
                }
            }
        }
    }


    static class FastScanner {
        BufferedReader br;
        StringTokenizer st;

        public FastScanner() {
            try {
                br = new BufferedReader(new InputStreamReader(System.in));
                // br = new BufferedReader(new FileReader("chat.txt"));
                st = new StringTokenizer("");
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        public String next() {
            if (st.hasMoreTokens())
                return st.nextToken();
            try {
                st = new StringTokenizer(br.readLine());
            } catch (Exception e) {
                e.printStackTrace();
            }
            return st.nextToken();
        }

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

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

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

        public String nextLine() {
            String line = "";
            try {
                line = br.readLine();
            } catch (Exception e) {
                e.printStackTrace();
            }
            return line;
        }

        public char nextChar() {
            return next().charAt(0);
        }

        public Integer[] nextIntegerArray(int n) {
            Integer[] a = new Integer[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public int[] nextIntArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        public long[] nextLongArray(int n) {
            long[] a = new long[n];
            for (int i = 0; i < n; i++)
                a[i] = nextLong();
            return a;
        }

        public char[] nextCharArray() {
            return nextLine().toCharArray();
        }
    }

}

/*class Pair implements Comparable<Pair> {

    int V;
    int H;

    public Pair(int count, int val) {
        this.V = count;
        this.H = val;
    }

    public void setV(int v) {
        V = v;
    }

    public void setH(int h) {
        H = h;
    }

    @Override
    public int compareTo(Pair o) {
         if(this.V != o.V)
            return Integer.compare(this.V, o.V);
         else
             return Integer.compare(this.H, o.H);
    }

    public boolean equals(Pair o) {
        return this.H == o.H && this.V == o.V;
    }
}*/

class Pair {

    int V;
    int H;

    public Pair(int x, int y) {
        this.V = x;
        this.H = y;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Pair)) return false;
        Pair key = (Pair) o;
        return V == key.V && H == key.H;
    }

    @Override
    public int hashCode() {
        int result = V;
        result = 31 * result + H;
        return result;
    }

}

