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;

typedef long long ll;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
typedef vector<vi> vvi;
#define INF 10000000000000000
#define pb push_back
#define sz(a) int((a).size())
#define all(c) c.begin(), c.end()
#define tr(c, i) for (typeof(c).begin() i = c.begin(); i != c.end(); i++)
#define present(c, x) (c.find(x) != c.end())
#define cpresent(c, x) (find(all(c), x) != c.end())
ll mod = 1e9 + 7;

ll bigmod(ll base, ll power)
{

    if (power == 0)
        return 1;
    ll x = bigmod(base, power / 2);

    if (power % 2 == 0)
        return (x * x) % mod;
    return (x * x * base) % mod;
}

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