import java.util.Scanner;

public class Main {
	// 2-100
	public static void main(String args[]) {
		Scanner in = new Scanner(System.in);
		long a = in.nextLong();
		long b = in.nextLong();
		long c = in.nextLong();
		long d = in.nextLong();
		long firstA = a*c;
		long firstB = a*d;
		long SecondA = b*c;
		long SecondB = b*d;
		System.out.println(Math.max(Math.max(firstA, firstB),Math.max(SecondA, SecondB)));
	}

}
/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