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: Time Limit Exceeded)

N = gets.to_i
line = gets
data = line.split(" ")
one = Array.new
two = Array.new
four = Array.new
data.each do |item|
  a = item.to_i
  if !one.include?(a)
    one << a
  else
    if !two.include?(a)
      one.delete(a)
      two << a
    else
      four << a
    end
  end
end
if two.empty?
  puts 0
else
  two.sort!{|a, b| b <=> a }
  max = two[0]
  if four.include?(max)
    puts max * max
  else
    puts max * two[1]
  end
end