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 Perl (v5.18.2) (judge verdict: Wrong Answer)

$N = <>;
@A = split(/ /, <>);
%cnt; # 同じ棒の長さの本数と値のhash
foreach $key (@A){
    if ($cnt{$key}) {
        $cnt{$key}=$cnt{$key}+1;
    } else {
        $cnt{$key}=1;
    }
}

$edge1 = 0;
$edge2 = 0;
foreach $key (reverse(sort(keys(%cnt)))){ # sortしてからじゃないとreverseできない
    if ($cnt{$key} >= 4) {
        $edge1 = $key if $edge1 < $key;
        $edge2 = $key if $edge2 < $key;
    } elsif ($cnt{$key} >= 2) {
        if ($edge1 < $key) {
            $edge1 = $key;
        } elsif ($edge2 < $key) {
            $edge2 = $key;
        }
    }
}


if (!$long1 || !$long2) { # どちらか0だと長方形を作れない
    print 0;
} else {
    print $long1 * $long2;
}