import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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 scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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 scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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 scan = new Scanner(System.in); scan new Scanner(System.in) long a = scan.nextInt(); a scan.nextInt() scan.nextInt scan long b = scan.nextInt(); b scan.nextInt() scan.nextInt scan long c = scan.nextInt(); c scan.nextInt() scan.nextInt scan long d = scan.nextInt(); d scan.nextInt() scan.nextInt scan scan.close() scan.close scan long max = a * c; 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 scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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 scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long 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);
    }
    
}