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)

gets
aa = gets.split.map(&:to_i).sort

a_count = Hash.new(0)
for a in aa
  a_count[a] = a_count[a] + 1
end

selection = []
for a, count in a_count
  if count >= 2
    selection << {"n" => a, "count" => count}
  end
end

if selection.size >= 2
  sorted_selection = selection.sort{|a1, a2| a1["n"] <=> a2["n"] }.reverse
  x = 0
  y = 0
  if sorted_selection[0]["count"] >= 4
    x = sorted_selection[0]["n"]
    y = sorted_selection[0]["n"]
  else
    x = sorted_selection[0]["n"]
    y = sorted_selection[1]["n"]
  end 
  puts x*y
else
  puts 0
end