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: Wrong Answer)

<?php
 fscanf(STDIN,"%d",$n);
 $a_li = explode(" ",trim(fgets(STDIN)));
 $count_hen = array();
 foreach($a_li as $a){
   $count_hen[$a]++;
 }

arsort($count_hen);
$x = '';
$y = '';

foreach($count_hen as $k=>$c){
  if($c>=4){
    echo $k*$k;
    exit;
  }elseif($c>=2){
    if($x!='' && $y!=''){
      	break;
    }elseif($x==''){
	    $x = $k;
    }else{
      $y = $k;
    }
  }
}

echo $x*$y;