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;

void solve(std::istream &in, std::ostream &out);

int main() {
#ifdef LOCAL
  freopen("../IO/b.in", "r", stdin);
//  freopen("../IO/b.out", "w", stdout);
#else
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);
  std::cout.tie(nullptr);
#endif
  solve(std::cin, std::cout);
  return 0;
}


void solve(std::istream &in, std::ostream &out) {
  int64_t a[4];
  for (int i = 0; i < 4; ++i) in >> a[i];
  int64_t mx = numeric_limits<int64_t>::min();
  for (int i = 0; i < 2; ++i) {
    for (int j = 2; j < 4; ++j) {
      mx = max(mx, a[i] * a[j]);
    }
  }
  if (a[0] <= 0 && 0 <= a[1] || a[2] <= 0 && 0 <= a[3]) {
    mx = max(mx, (int64_t)0);
  }
  out << mx << '\n';
}