import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long a = sc.nextLong(); a sc.nextLong() sc.nextLong sc long b = sc.nextLong(); b sc.nextLong() sc.nextLong sc long c = sc.nextLong(); c sc.nextLong() sc.nextLong sc long d = sc.nextLong(); d sc.nextLong() sc.nextLong sc long ans = a*c; ans a*c a c if (ans < (a*d)) {
            ans = a*d;
        } ans < (a*d) ans (a*d) a d {
            ans = a*d;
        } ans = a*d ans a*d a d if (ans < (b*c)) {
            ans = b*c;
        } ans < (b*c) ans (b*c) b c {
            ans = b*c;
        } ans = b*c ans b*c b c if (ans < (b*d)) {
            ans = b*d;
        } ans < (b*d) ans (b*d) b d {
            ans = b*d;
        } ans = b*d ans b*d b d System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();
        long ans = a*c;
        if (ans < (a*d)) {
            ans = a*d;
        }
        if (ans < (b*c)) {
            ans = b*c;
        }
        if (ans < (b*d)) {
            ans = b*d;
        }

        System.out.println(ans);
    }
}
