import java.util.*;
public class Main {

	public static void main(String[] args) {
		Scanner sc=new Scanner(System.in);
		long a=sc.nextLong();
		long b=sc.nextLong();
		long c=sc.nextLong();
		long d=sc.nextLong();
		long ac=a*c;
		long ad=a*d;
		long bc=b*c;
		long bd=b*d;
		System.out.println(Math.max(Math.max(ac, bd),Math.max(ad, bc)));
	}

}

/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