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 n;
    scanf("%d", &n);
    int a[n];
    int i = 0;
    while(i<n)
    {
        scanf("%d", &a[i]);
        i++;
    }
    int l = sizeof(a)/sizeof(a[0]);
    sort(a,a+l);
    int p1 = 0,p2 = 0;
    i = n;
    int f = 0;
    while(i>0)
    {
        if(a[i] == a[i-1] )
        {
            p1 = a[i];
            f = i;
            break;
        }
        i-=1;
    }
    i = n;
    while(i>0)
    {
        if(a[i] == a[i-1] && i!=f && i!=f-1)
        {
            p2 = a[i];
            break;
        }
        i = i-1;
    }
    printf("%d %d %d", p1,p2,p1*p2);
}