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>
#include<stdlib.h>
#include<string.h>

int main(void)
{
	int n, i, choice = 2;
	long int a[100000] = {};
	int buff, max = 0;
	int s = 1;

	scanf("%d", &n);

	for (i = 0; i < n; i++) {
		scanf("%d", &buff);
		if (buff > max) {
			max = buff;
		}
		a[buff]++;
	}

	for (i = max; i >= 0 && choice != 0; i--) {
		if (a[i] >= 2) {
			s *= i;
			choice--;
		}
	}

	if (choice == 0) {
		printf("%d", s);
	}
	else {
		printf("0");
	}
}