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 argc, char** argv) {
	long long n;
	cin>>n;
	long long  a[n]={0};
	 
	for(int i=0;i<n;i++) {
		cin>>a[i];
	}
   sort(a,a+n);
   long long t1=0,t2=0;
   for(int i=n-1;i>0;i--){
   	
   	if(a[i]==a[i-1]){
   		t1=a[i];
		break;
	   }
   	
   }
   for(int i=n-1;i>0;i--){

	   
   	if(a[i]==a[i-1]&&a[i]<t1){
   		t2=a[i];
		  break;	
	   }
   }
   
   if(t1==0||t2==0)  cout<<"0"<<endl;;
    if(t1!=0&&t2!=0)cout<<t1*t2<<endl;
	return 0;
}