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<cstdio>
#include<iostream>
#include<ctime>
#include<string>
#include<algorithm>
#include<cmath>
#include<vector>
int sides[100010];
int n;
using namespace std;
int main()
{
	scanf("%d",&n);
	int j=0;
	for(int i=0;i<n;i++)
	{
		int t;
		scanf("%d",&t);
		sides[i]=t;
	}
	sort(sides,sides+j);
	int one=-1;
	for(int i=n-1;i>=1;i--)
	{
		if(sides[i]==sides[i-1])
		{
			if(one==-1)
			{
				one=sides[i];
				i--;
			}
			else
			{
				printf("%lld",(long long)one*sides[i]);
				return 0;
			}
		}
	}
	printf("0");
	return 0;
}