import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner(System.in);
        List<Integer> list = new ArrayList<Integer>();
        int a = sc.nextInt();
        int b = sc.nextInt();
        int c = sc.nextInt();
        int d = sc.nextInt();
        long a1 = (long)a*c;
        long a2 = (long)a*d;
        long a3 = (long)b*c;
        long a4 = (long)b*d;
        //System.out.println(a1+" "+a2+" "+a3+" "+a4+" ");
        System.out.println(Math.max(a1,Math.max(a2,Math.max(a3,a4))));
    }
}

/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