import java.util.Scanner;
 
public class Main {
	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 prod = Long.MIN_VALUE;
      prod = Math.max(prod, b*d);
      prod = Math.max(prod, a*c);
        prod = Math.max(prod, Math.min(b,d) * Math.max(a,c));
      System.out.println(prod);
	}
}
/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