import java.io.PrintWriter;
import java.util.Scanner;

public class Main {

    void solve(Scanner in, PrintWriter out) {
        long a = in.nextInt();
        long b = in.nextInt();
        long c = in.nextInt();
        long d = in.nextInt();
        out.println(Math.max(a * c, Math.max(a * d, Math.max(b * c, b * d))));
    }

    public static void main(String[] args) {
        try(Scanner in = new Scanner(System.in);
            PrintWriter out = new PrintWriter(System.out)) {
            new Main().solve(in, out);
        }
    }
}

/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