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
$n = trim(fgets(STDIN));
$a = explode(" ", trim(fgets(STDIN)));
foreach($a as $num){
    @$map[$num]++;
}
$array = [];
foreach($map as $num => $count){
    for($i = 2; $i <= $count; $i+=2){
        $array[] = $num;
    }
}
if(count($array) >= 2){
    rsort($array);
    echo $array[0] * $array[1];
}else{
    echo 0;
}