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 i,idx,k,j,n,a[100002],mx=0;
    map<int,int>m;
    cin>>n;
    idx=0;
    for(i=0;i<n;i++){cin>>a[i];}
    sort(a,a+n,greater<int>());
    for(i=0;i<n;i++){m[a[i]]++;}
    for(j=0;j<n;j++){
     for(k=j+1;k<n;k++){
   if(m[a[j]]>=4){mx=max(mx,a[j]*a[j]);idx=1;break;}
if(m[a[j]]>=2&&m[a[k]]>=2){
  if(a[j]!=a[k])
    {mx=max(mx,a[k]*a[j]);idx=1;break;}
            }
          }
        if(idx==1){break;}
      }
   if(mx==0){cout<<"0\n";}
    else{
    cout<<mx<<endl;}

     


}