import java.util.Scanner;

public class Main {

	public static void main(String[] args) throws Exception {
		Scanner sc = new Scanner(System.in);

		long a = sc.nextLong();
		long b = sc.nextLong();
		long c = sc.nextLong();
		long d = sc.nextLong();

		long ans = 0;
		if(a < 0 && b <= 0) {
			if(c < 0) {
				ans = a * c;
				System.out.print(ans);
			}else{
				ans = b * c;
				System.out.print(ans);
			}
		}else if(c < 0 && d <= 0) {
			if(a < 0) {
				ans = a * c;
				System.out.print(ans);
			}else{
				ans = a * d;
				System.out.print(ans);
			}
		}else {
			if(a * c > b * d) {
				System.out.print(a * c);
			}else {
				System.out.print(b * d);
			}
		}

		sc.close();
	}
}
/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