import java.util.*;
import java.lang.Math;

public class Main{

public static void main(String[] args){
Scanner scanner1 = new Scanner(System.in);
Scanner scanner2 = new Scanner(System.in);
long a=scanner1.nextLong();
long b=scanner1.nextLong();
long c=scanner1.nextLong();
long d=scanner1.nextLong();
long t=a*c;

long e=Math.max(a*c,Math.max(a*d,Math.max(b*c,b*d)));
System.out.println(e);



}
}
/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