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 Ruby (2.3.3) (judge verdict: Accepted)

sticks = Hash.new(0)

gets
gets.split.each {|a| sticks[a.to_i] += 1}

selected = sticks.select {|length, num| num >= 2}
             .sort_by {|length, num| -length}.take(2)
s = selected.size
result = if s >= 1 && selected[0][1] >= 4
           selected[0][0] ** 2
         elsif s >= 2 && selected[0][1] >= 2 && selected[1][1] >= 2
           selected[0][0] * selected[1][0]
         else
           0
         end
         
puts result