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 (GCC 5.4.1) (judge verdict: Runtime Error)

#include <stdio.h>

int main() {
    int arr[10000], i, j, k = 0, n, temp, c[10000], l;
    scanf("%d", &n);
    for (i = 0; i < n; i++)
        scanf("%d", &arr[i]);
    for (i = 0; i < n; i++)
        for (j = 0; j < n -i;j++)
        {
            if(arr[j+1] < arr[j])
            {
                temp = arr[j+1];
                arr[j+1] = arr[j];
                arr[j] = temp;
            }
        }
   for (i = 0; i < n/2; i++)
   { 
       for (j = 0; j < n - 1; j++)
        if (arr[j] == arr[j+1])
        {
            c[k] = arr[j];
            k++;
        }
        l = k;
        k = 0;
   }
   if (l != 0)
    printf("%d", c[l-1] * c[l-2]);
    else
        printf("0");
	return 0;
}