import java.util.Scanner;

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

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

        if (a == 0 && b == 0 || c == 0 && d == 0) {
            System.out.println(0);
            return;
        } else if (a > 0 && d < 0) {
            System.out.println(a * d);
            return;
        } else if (b < 0 && c > 0) {
            System.out.println(b * c);
            return;
        } else if (a == 0 && d < 0 || c == 0 && b < 0) {
            System.out.println(0);
            return;
        } else if (a >= 0 || c >= 0) {
            System.out.println(b * d);
            return;
        } else if (a < 0 && b > 0 && c < 0 && d > 0) {
            System.out.println(Math.max(a * c, b * d));
            return;
        } else {
            System.out.println(a * c);
            return;
        }

    }

}

/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