import java.util.*;
class Main{
  public static void main(String args[]){
    Scanner scan = new Scanner(System.in);
	long a=scan.nextInt(),b=scan.nextInt(),c=scan.nextInt(),d=scan.nextInt();
    long  x1,x2;
    x1=Math.max(a*c,a*d);
    x2=Math.max(b*c,b*d);
    x1=Math.max(x1,x2);
    System.out.println(x1);
  }
}
/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