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: Accepted)

#!/usr/bin/perl


$line = 0;
while (<>) {
    chomp;
    if($line == 0) {
        $n = $_;
    } else {
        @a = split /\s+/, $_
    }
    $line++;
}

foreach (@a) {
    $e{$_}++;
}

foreach (sort {$b <=> $a} keys %e) {
    if($e{$_} >= 2) {
        push @h, $_;
        if($#h >= 1) {
            print $h[0] * $h[1], "\n";
            exit;
        }
        if($e{$_} >= 4) {
            print $_ * $_, "\n";
            exit;
        }
    }
}

print "0\n";