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 = STDIN.gets.chomp.to_i
a = STDIN.gets.chomp.split.collect do |e| e.to_i end
h = Hash.new

a.each do |e|
  if h.include?(e)
    h[e] += 1
  else
    h[e] = 1
  end
end

keys = h.keys.sort {|x, y| y <=> x }

x = -1
y = -1

keys.each do |k|
  if x != -1 && y != -1
    break
  end

  if (x == -1 && h[k] >= 2)
    x = k
    h[k] -= 2
  end

  if (x != -1 && y == -1 && h[k] >= 2)
    y = k
    h[k] -= 2
  end
end

if (x == -1 || y == -1)
  puts 0
else
  puts x * y
end