import java.util.Scanner;

public class Main{
  public static void main(String[] args){
    Scanner scan = new Scanner(System.in);
    long a = scan.nextLong();
    long b = scan.nextLong();
    long c = scan.nextLong();
    long d = scan.nextLong();
    long max = 0;
    
    if(b<=0 && d<=0){
      System.out.println(a*c);
    }else if(a>=0 && c>=0){
      System.out.println(b*d);
    }else if(b<=0 && c>=0){
      System.out.println(b*c);
    }else if(a>=0 && d<=0){
      System.out.println(a*d);
    }else{
      long ac = a*c;
      long bd = b*d;
      if(ac >= bd){
        System.out.println(ac);
      }else{
        System.out.println(bd);
      }
    }
    
  }
}
    
/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