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: Wrong Answer)

N = gets.to_i
a_list = gets.split.map(&:to_i)
table = Hash.new { 0 }
a_list.each do |a|
  table[a] += 1
end
sorted = table.sort_by { |k, v| -k }.select { |k, v| v >= 2 }
if sorted.size == 0
  puts '0'
elsif sorted.size == 1 && sorted[0][1] < 4
  puts '0'
else
  ans = if sorted[0][1] >= 4
    sorted[0][0] * 2
  else
    sorted[0][0] * sorted[1][0]
  end
  puts ans
end