import java.util.Scanner;

 
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 temp1 = Math.max(a * c, a * d);
		long temp2 = Math.max(b * c, b * d);
		
		System.out.println(Math.max(temp1, temp2));
		sc.close();
	}
}



/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