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: Wrong Answer)

#include <stdio.h>
#include <stdlib.h>

int cmp(const void* a, const void* b)
{
	return *(int*)b - *(int*)a;
}

int main()
{
	int i, imax, bow[100001] = { 0 };
	int tmp = 0, hen = 0, takasa = 0;

	scanf("%d", &imax);

	for (i = 0; i < imax; i++) {
		scanf("%d", &bow[i]);
	}

	qsort((void*)bow, imax, sizeof(bow[0]), cmp);

	for (i = 0; i < imax; i++) {
		if (tmp == bow[i]) {
			if (hen == 0) {
				hen = bow[i];
				tmp = 0;
			} else {
				takasa = bow[i];
				break;
			}
		} else {
			tmp = bow[i];
		}
	}


	printf("%d", hen * takasa);
	return 0;
}