import java.util.Scanner;

/**
 * @author yadavd5
 *
 */
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 first= a*c;
		long  second = a*d;
		long third = b*c;
		long fourth = b*d;
		long firstmax = Math.max(first, second);
		long secondman = Math.max(third, fourth);
		System.out.println(Math.max(firstmax, secondman));
	}

}
/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