import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        long a = scan.nextInt();
        long b = scan.nextInt();
        long c = scan.nextInt();
        long d = scan.nextInt();
        scan.close();
        long max = a * c;
        
        max = Math.max(max, a * d);
        max = Math.max(max, b * c);
        max = Math.max(max, b * d);

        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