import java.util.*;
public class Main{

    public static void main(String[]args){
        Scanner sc = new Scanner(System.in);
        long a=sc.nextInt();
        long b=sc.nextInt();
        long c=sc.nextInt();
        long d=sc.nextInt();
        long val1=a*c;
        long val2=a*d;
        long val3=b*c;
        long val4=b*d;
        long max=Math.max(Math.max(Math.max(val1,val2),val3),val4);
        System.out.println(max);
        }
    }

/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