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)

n = gets.chomp.to_i
a = gets.split.map(&:to_i)
hash = {}
a.each do |i|
  if hash.has_key?(i)
    hash[i] += 1
  else
    hash[i] = 0
  end
end

array = []
hash.each do |ngo|
  if ngo[1] >= 3
    array.push(ngo[0]) 
    array.push(ngo[0])
  elsif ngo[1] > 0   
    array.push(ngo[0])
  end
end
array.sort!{|a,b|b<=>a}
puts array.size > 1 ? array[0] * array[1] : 0