import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;


public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        long a = sc.nextInt();
        long b = sc.nextInt();
        long c = sc.nextInt();
        long d = sc.nextInt();
        List<Long>str = new ArrayList<>();
        str.add(a*c);
        str.add(a*d);
        str.add(b*c);
        str.add(b*d);
        Collections.sort(str,Collections.reverseOrder());
        System.out.println(str.get(0));
    }
}

/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