
import java.util.*;
public class Main
{
  public static void main(String args[])
  {
    Scanner sc=new Scanner(System.in);
   long a=sc.nextInt();
    long b=sc.nextInt();
    long c=sc.nextInt();
    long d=sc.nextInt();
    long arr[]=new long[4];
    arr[0]=a*c;
    arr[1]=a*d;
    arr[2]=b*c;
    arr[3]=b*d;
    Arrays.sort(arr);
    System.out.println(arr[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