import java.math.BigInteger;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        long a = sc.nextLong();
        long b = sc.nextLong();
        long c = sc.nextLong();
        long d = sc.nextLong();

        BigInteger ac = BigInteger.valueOf(a).multiply(BigInteger.valueOf(c));
        BigInteger ad = BigInteger.valueOf(a).multiply(BigInteger.valueOf(d));

        BigInteger result1 = ac.max(ad);

        BigInteger bc = BigInteger.valueOf(b).multiply(BigInteger.valueOf(c));
        BigInteger bd = BigInteger.valueOf(b).multiply(BigInteger.valueOf(d));

        BigInteger result2 = bc.max(bd);

        System.out.println(result1.max(result2));

    }
}
/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