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++ (GCC 9.2.1) (judge verdict: Wrong Answer)

                                        //BISMILLAHIR RAHMANIR RAHIM
                                          //By the name of ALLAH
#include<iostream>
#include<algorithm>
#include<vector>
#include<set>
#include<iterator>
#include<numeric>
#define pi acos(-1.0)
using namespace std;
bool f(long long int x,long long int y)
{
    return x>y;
}
void solve()
{
    long long n,a[100000],i,j,p=0,q=0;
    cin>>n;
    for(i=0;i<n;i++){
        cin>>a[i];
    }
    sort(a,a+n,f);
    for(i=0;i<n;i++){
        if(a[i]==a[i+1]){
            p=a[i];
            break;
        }
    }
    for(j=i+1;j<n;j++){
        if(a[j]==a[j+1] && a[j]!=p){
            q=a[j];
            break;
        }
    }
    cout<<p*q<<endl;

}
int main()
{
    solve();
    return 0;
}