import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(
                new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer(br.readLine());
        br.close();
        long a = Integer.parseInt(st.nextToken()),
                b = Integer.parseInt(st.nextToken()),
                c = Integer.parseInt(st.nextToken()),
                d = Integer.parseInt(st.nextToken()),
                max = Math.max(Math.max(a * c, a * d), Math.max(b * c, b * d));

        if ((a <= 0 && b >= 0) || (c <= 0 && d >= 0)) {
            max = Math.max(max, 0);
        }

        System.out.println(max);
    }
}

/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