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 PHP7 (7.0.15) (judge verdict: Accepted)

<?php

// define('DEBUG', true);
define('DEBUG', false);


fscanf(STDIN, "%d", $N);
$a = explode(" ", trim(fgets(STDIN)));
// var_dump($a);
$arr = array();
$sq = array();
$target = 0;

rsort($a);

for ($i = 0; $i < $N; $i++) {
    $arr[$a[$i]]++;
    if ($arr[$a[$i]] == 2) {
        $sq[$target] = $a[$i];
        $arr[$a[$i]] -= 2;
        $target++;
        if ($target >= 2) {
            echo ($sq[0] * $sq[1]) . PHP_EOL;
            exit;
        }
    }
}

echo "0\n";