import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    }
    
    private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    }
    
    private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    }
} Main public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    } main {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    } long[] abcd = new long[4]; abcd new long[4] 4 try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        } {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        } Scanner s = new Scanner(System.in) Scanner s = new Scanner(System.in) new Scanner(System.in) for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            } int i = 0; int i = 0; i 0 i < 4 i 4 i++ i++ i {
                abcd[i] = s.nextLong();
            } {
                abcd[i] = s.nextLong();
            } abcd[i] = s.nextLong() abcd[i] abcd i s.nextLong() s.nextLong s System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3])) System.out.println System.out System System.out max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]) max abcd[0] * abcd[2] abcd[0] abcd 0 abcd[2] abcd 2 abcd[0] * abcd[3] abcd[0] abcd 0 abcd[3] abcd 3 abcd[1] * abcd[2] abcd[1] abcd 1 abcd[2] abcd 2 abcd[1] * abcd[3] abcd[1] abcd 1 abcd[3] abcd 3 String[] args args private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    } max {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    } long m1 = Math.max(p, q); m1 Math.max(p, q) Math.max Math p q long m2 = Math.max(m1, r); m2 Math.max(m1, r) Math.max Math m1 r return Math.max(m2, s); Math.max(m2, s) Math.max Math m2 s long p p long q q long r r long s s public class Main {
    public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    }
    
    private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    }
    
    private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        long[] abcd = new long[4];
        try (Scanner s = new Scanner(System.in)) {
            for(int i = 0; i < 4; i++) {
                abcd[i] = s.nextLong();
            }
            System.out.println(max(abcd[0] * abcd[2], abcd[0] * abcd[3], abcd[1] * abcd[2], abcd[1] * abcd[3]));
        }
    }
    
    private static long max(long p, long q, long r, long s) {
        long m1 = Math.max(p, q);
        long m2 = Math.max(m1, r);
        return Math.max(m2, s);
    }
}
