import java.util.*;
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 e =a*c;
    long f =b*d;
    long g =a*d;
    long h =b*c;
    long ans =Math.max(e,f);
    ans =Math.max(ans,g);
    ans =Math.max(ans,h);
    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