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)

chomp($n=<>);
chomp($s=<>);
@ary=split/ /,$s;
@ary=sort{$b <=> $a}@ary;
%hash=();
for($i=0;$i<=$#ary;$i++){
	$hash{$ary[$i]}++;
    if($hash{$ary[$i]} == 2){
    	push @area,$ary[$i];
    }elsif($hash{$ary[$i]} == 4){
    	push @area,$ary[$i];
    }
    $length = @area;
    if($length >= 2){
    	break;
    }
}

print $area[0] * $area[1];