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>
using namespace std;
using ll         = long long;
constexpr ll MOD = 1000000007;
#define REP(i, n) for (ll i = 0; i < (n); i++)
#define REP2(i, x, n) for (ll i = x; i < (n); i++)
#define PR(x) cout << (x) << "\n"
#define PS(x) cout << (x) << " "
#define PRYES(x) PR((x) ? "Yes" : "No")
const long long INF = numeric_limits<long long>::max();
// SourceTest用出力マクロ
#ifdef SOURCE_TEST
#define SPR(x) PR(x)
#define SPS(x) PS(x)
#else
#define SPR(x) \
    {}
#define SPS(x) \
    {}
#endif
int main() {
    ll a, b, c, d;
    cin >> a >> b >> c >> d;

    vector<ll> answers;
    answers.push_back(a * c);
    answers.push_back(a * d);
    answers.push_back(b * c);
    answers.push_back(b * d);
    sort(answers.begin(), answers.end());

    PR(answers[3]);

    return 0;
}