import java.util.Scanner;
class Main{
public static void main(String[]args){
Scanner input=new Scanner(System.in);
  long a=input.nextInt();
  long b=input.nextInt();
  long c=input.nextInt();
  long d=input.nextInt();
  long max=a*c>b*d?a*c:b*d;
  max=max>a*d?max:a*d;
  max=max>b*c?max:b*c;
    System.out.println(max);
}
}
/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