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 h = a*c;
    long i = a*d;
    long j = b*c;
    long k = b*d;
    
    long x = Math.max(h,i);
    long y = Math.max(j,k);
    long z = Math.max(x,y);
    
    System.out.println(z);
  }
}
    
    
    
/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