import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    } main {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long a = Long.parseLong(sc.next()); a Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc long b = Long.parseLong(sc.next()); b Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc long c = Long.parseLong(sc.next()); c Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc long d = Long.parseLong(sc.next()); d Long.parseLong(sc.next()) Long.parseLong Long sc.next() sc.next sc long max = Long.MIN_VALUE; max Long.MIN_VALUE Long Long.MIN_VALUE if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        } a - b != 0 a - b a b 0 {
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        } if(a == 0) a += 1; a == 0 a 0 a += 1 a 1 if(b == 0) b -= 1; b == 0 b 0 b -= 1 b 1 if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        } c - d != 0 c - d c d 0 {
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        } if(c == 0) c += 1; c == 0 c 0 c += 1 c 1 if(d == 0) d -= 1; d == 0 d 0 d -= 1 d 1 max = Math.max(max, a * c) max Math.max(max, a * c) Math.max Math max a * c a c max = Math.max(max, a * d) max Math.max(max, a * d) Math.max Math max a * d a d max = Math.max(max, b * c) max Math.max(max, b * c) Math.max Math max b * c b c max = Math.max(max, b * d) max Math.max(max, b * d) Math.max Math max b * d b d System.out.println(max) System.out.println System.out System System.out max String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = Long.parseLong(sc.next());
        long b = Long.parseLong(sc.next());
        long c = Long.parseLong(sc.next());
        long d = Long.parseLong(sc.next());
        long max = Long.MIN_VALUE;
        if(a - b != 0){
            if(a == 0) a += 1;
            if(b == 0) b -= 1;
        }
        if(c - d != 0){
            if(c == 0) c += 1;
            if(d == 0) d -= 1;
        }
        max = Math.max(max, a * c);
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);
        System.out.println(max);
    }
}
