Problem:
Score : 200 points

Problem Statement

Given are integers a,b,c and d.
If x and y are integers and a \leq x \leq b and c\leq y \leq d hold, what is the maximum possible value of x \times y?

Constraints

-10^9 \leq a \leq b \leq 10^9

-10^9 \leq c \leq d \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

a b c d

Output

Print the answer.

Sample Input 1

1 2 1 1

Sample Output 1

2

If x = 1 and y = 1 then x \times y = 1.
If x = 2 and y = 1 then x \times y = 2.
Therefore, the answer is 2.

Sample Input 2

3 5 -4 -2

Sample Output 2

-6

The answer can be negative.

Sample Input 3

-1000000000 0 -1000000000 0

Sample Output 3

1000000000000000000

Solution in C++ (GCC 9.2.1) (judge verdict: Accepted)

#include <bits/stdc++.h>
// #include <atcoder/all>
using namespace std;
// using namespace atcoder;
 
#define rp(i, k, n) for (int i = k; i < n; i++)
using ll = long long;
using ld = double;

template<class T>inline bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>inline bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
const ll INF = 1ll << 60;
const ll MOD = 1e9 + 7ll;
const double PI=3.14159265358979323846;

int main() {
    ll a, b, c, d;
    cin >> a >> b >> c >> d;
    cout << max({a*c, a*d, b*c, b*d}) << endl;
    return 0;
}