Problem:
Score : 300 points

Problem Statement

We have N sticks with negligible thickness.
The length of the i-th stick is A_i.

Snuke wants to select four different sticks from these sticks and form a rectangle (including a square), using the sticks as its sides.
Find the maximum possible area of the rectangle.

Constraints

4 \leq N \leq 10^5

1 \leq A_i \leq 10^9

A_i is an integer.

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 ... A_N

Output

Print the maximum possible area of the rectangle.
If no rectangle can be formed, print 0.

Sample Input 1

6
3 1 2 4 2 1

Sample Output 1

2

1 \times 2 rectangle can be formed.

Sample Input 2

4
1 2 3 4

Sample Output 2

0

No rectangle can be formed.

Sample Input 3

10
3 3 3 3 4 4 4 5 5 5

Sample Output 3

20

Solution in C++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
using namespace std;

int N;
int arr[100000];
long long area;

int main(){
  cin >> N;
  int first,second;
  for (int i=0;i<N;i++){
    cin >> arr[i];
  }
  sort(arr,arr+N);
  for (int i=N-1;i>0;i--){
     if (arr[i]==arr[i-1]){
        if (first==0){
          first = arr[i];
        }
        else if(second==0 && arr[i]!=first){
          second = arr[i];
          break;
        }
     }
  }
  area = first*second;
  cout << area;
  return 0;
}