import java.util.Scanner;

public class Main {
	public static void main(String args[]) {
		Scanner stdIn = new Scanner(System.in);
		long a = stdIn.nextInt();
		long b = stdIn.nextInt();
		long c = stdIn.nextInt();
		long d = stdIn.nextInt();
		
		System.out.println(Math.max(a * c, Math.max(a * d, Math.max(b * c, b * d))));
	}
}
/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