import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        long a = nextInt(scanner);
        long b = nextInt(scanner);
        long c = nextInt(scanner);
        long d = nextInt(scanner);
        System.out.println(Math.max(a * c, Math.max(a * d, Math.max(b * c, b * d))));
    }

    private static int nextInt(Scanner scanner) {
        return Integer.parseInt(scanner.next());
    }

    private static long nextLong(Scanner scanner) {
        return Long.parseLong(scanner.next());
    }

    private static float nextFloat(Scanner scanner) {
        return Float.parseFloat(scanner.next());
    }

    private static double nextDouble(Scanner scanner) {
        return Double.parseDouble(scanner.next());
    }


}


class UnionFind {
    int[] parent;

    UnionFind(int n) {
        parent = new int[n];
        Arrays.fill(parent, -1);
    }

    int find(int x) {
        if (parent[x] < 0) {
            return x;
        } else {
            parent[x] = find(parent[x]);
            return parent[x];
        }
    }

    void unite(int x, int y) {
        int rootX = find(x);
        int rootY = find(y);
        if (rootX == rootY) {
            return;
        }

        if (parent[rootX] > parent[rootY]) {
            int temp = rootX;
            rootX = rootY;
            rootY = temp;
        }
        parent[rootX] += parent[rootY];
        parent[rootY] = rootX;
    }

}

/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