import java.util.*;

public class Main{
	public static void main(String[] args){
    	Scanner sc = new Scanner(System.in);
      	while(sc.hasNext()){
        	long a = sc.nextInt();
          	long b = sc.nextInt();
          	long c = sc.nextInt();
          	long d = sc.nextInt();
          	long ans = Math.max(Math.max(a*c,a*d), Math.max(b*c, b*d));
          	System.out.println(ans);
        }
    }
}
/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