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 main(){
     int n,t;
     vector<int> rec;
     cin >> n;
     priority_queue<int> q;
     for(int i=0;i<n;i++){
        cin >> t;
        q.push(t);
     }
     for(int i=0;i<n;i++){
        t=q.top();
        q.pop();
        if(q.empty())
            break;
        if(q.top()==t){
            rec.push_back(t);
            q.pop();
            i++;
            if(rec.size()==2)
                break;
        }
     }
    if(rec.size()==2)
        cout << rec[rec.size()-1]*rec[rec.size()-2];
    else
        cout << '0';
}