import java.util.*;
public class Main {
    public static void main(String args[]) {
        Scanner sc = new Scanner(System .in);
        int a = sc.nextInt();
        int b = sc.nextInt();
        long max1 = a>b?a:b;
        long min1 = a<=b?a:b;
        int c = sc.nextInt();
        int d = sc.nextInt();
        long max2 = c>d?c:d;
        long min2 = c<=d?c:d;
        long max = Math.max(Math.max(Math.max(max1*max2,min1*min2),max1*min2),min1*max2);
        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