import java.util.Scanner;


public class Main {


	public static void main(String[] args)  {
		Scanner sc = new Scanner(System.in);
		Long a = Long.parseLong(sc.next());
		Long b = Long.parseLong(sc.next());
		Long c = Long.parseLong(sc.next());
		Long d = Long.parseLong(sc.next());
		
		Long max = -1000000000000000000l;
		
		max = Math.max(max,a * c);
		max = Math.max(max,a * d);
		max = Math.max(max,b * c);
		max = Math.max(max,b * d);
		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