import java.util.Scanner;

public class Main {
    static Scanner stdIn = new Scanner(System.in);
    public static void main(String[] args){
        long a = stdIn.nextLong();
        long b = stdIn.nextLong();
        long c = stdIn.nextLong();
        long d = stdIn.nextLong();

        long max = Long.MIN_VALUE;
        if(max < a * c)
            max = a * c;
        if(max < a * d)
            max = a * d;
        if(max < b * c)
            max = b * c;
        if(max < b * d)
            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