import java.util.Scanner;

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

/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