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 a1 = a * c;
        long a2 = a * d;
        long a3 = b * c;
        long a4 = b * d;
                
        long b1 = Math.max(a1, a2);
        long b2 = Math.max(a3, a4);
        long ans = Math.max(b1, b2);
        
        System.out.println(ans);      
        
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz