import java.util.*;
class Main{
    static Scanner sr = new Scanner(System.in);

    public static void main(String[] args) throws java.lang.Exception {
        long a = sr.nextLong();
        long b = sr.nextLong();
        long c = sr.nextLong();
        long d = sr.nextLong();
        long ans[]=new long[4];
        ans[0]=a*c;
        ans[1]=a*d;
        ans[2]=b*c;
        ans[3]=b*d;
        Arrays.sort(ans);
        System.out.println(ans[3]);


        }
    }



/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