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)

use v5.18; # strict say state
use warnings;
use List::Util qw(max);

chomp (my $n = <STDIN>);
chomp (my @a = split / /, <STDIN>);
my %h;
$h{$_}++ for @a;
my @s = sort {$b <=> $a} grep {$h{$_} >= 4} keys %h;
my @t = sort {$b <=> $a} grep {$h{$_} >= 2} keys %h;
my $ans = 0;
$ans = $s[0] * $s[0] if @s > 0;
$ans = max($ans, $t[0] * $t[1]) if @t > 1;
say $ans;