import java.util.*;
import java.io.*;


public class Main{

     public static void main(String []args){
        Scanner scanner = new Scanner(System.in);
        long n1= (long)scanner.nextInt();
        long n2= (long)scanner.nextInt();
        long n3= (long)scanner.nextInt();
        long n4= (long)scanner.nextInt();
        
        long arr[] = new long[4];
        
             arr[0] = n1*n3;
             arr[1] = n1*n4;
             arr[2] = n2*n3;
             arr[3] = n2*n4;
           
           
        Arrays.sort(arr);
    
         System.out.println(arr[arr.length-1]);
        
        
        
        //for(int i=0;i<n;i++)
        //int n= scanner.nextInt();
        //System.out.println()
     }
}
/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