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;
#define _GLIBCXX_DEBUG
#define rep(i, from, to) for (ll i = from; i < (to); ++i)
#define mp(x,y) make_pair(x,y)
#define all(x) (x).begin(),(x).end()
#define sz(x) (int)(x).size()
#define pb push_back
using ll = long long;
using ld=long double;
using vin=vector<int>;
using vvin=vector<vin>;
using vll=vector<ll>;
using vvll=vector<vll>;
using vst=vector<string>;
using P = pair<ll,ll>;
const int inf=1e9+7;
const ll INF=9e18;
template <typename T> bool chmin(T &a, const T& b){if(a > b){a = b;return true;}return false;}
template <typename T> bool chmax(T &a, const T& b){if(a < b){a = b;return true;}return false;}
template<class T> inline void Yes(T condition){ if(condition) cout << "Yes" << endl; else cout << "No" << endl; }
template<class T> inline void YES(T condition){ if(condition) cout << "YES" << endl; else cout << "NO" << endl; }
const int dx[4] = { 1, 0, -1, 0 };
const int dy[4] = { 0, 1, 0, -1 };

int main(){cout<<fixed<<setprecision(20);
		   ll a,b,c,d;
           cin>>a>>b>>c>>d;
           ll ans=-INF;
           chmax(ans,a*c);
           chmax(ans,a*d);
           chmax(ans,b*c);
           chmax(ans,b*d);
           cout<<ans<<endl;
}