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: Accepted)

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

int main()
{
	int n;
	cin>>n;
	int64_t a[n]={};
	for(int i = 0 ; i < n ; i++)
		cin>>a[i];
	sort(a , a+n , greater<int64_t>());
	int64_t x = 0 , y = 0;
	for(int i = 1 ; i < n ; i++)
	{

		if(a[i] == a[i-1])
		{
			if( x == 0)
				x = a[i];
			else if ( y == 0)
				y = a[i];
			i+=1;
		}
		if( x && y)
			break;
	}
	cout<< x * y <<"\n";
	return 0;
}