import java.util.*;

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        // xの範囲
        long a = sc.nextLong();
        long b = sc.nextLong();
        // yの範囲
        long c = sc.nextLong();
        long d = sc.nextLong();

        long resultA = a * c;
        resultA = resultA < a * d ? a * d : resultA;
        long resultB = b * c;
        resultB = resultB < b * d ? b * d : resultB;
        if (resultA < resultB) {
            System.out.println(resultB);
        } else {
            System.out.println(resultA);
        }
    }
}

/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