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 <iostream>
#include <algorithm>
using namespace std;
int main(){
	int n;
	long long int a[100000];
	cin >> n;
	for(int i = 0;i < n;i++){
		cin >> a[i];
	}
	sort(a, a + n);
	long long int l = 0, w = 0;
	int i = n - 1;
	while(i > 0){
		if(a[i] == a[i - 1]){
			l = a[i];
			i-=2;
			break;
		}else{
			i--;
		}
	}
	while(i > 0){
		if(a[i] == a[i - 1]){
			w = a[i];
			break;
		}else{
			i--;
		}
	}
	cout << l * w << endl;
}