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: Runtime Error)

n = gets.chomp.to_i
a = gets.chomp.split(' ').map(&:to_i)
side = []
ac = Array.new(10**9, 0)
is_asn = false

b = a.uniq.sort.reverse
a.each do |i|
  ac[i] += 1
end

b.each do |i|
  c = ac[i]
  if c >= 4
    if side.size == 1
      puts side[0] * i
      is_asn = true
      break
    else
      puts i * i
      is_asn = true
      break
    end
  elsif c >= 2 && c <= 4
    side << i
    if side.size == 2
      puts side[0] * side[1]
      is_asn = true
      break
    end
  end
end

puts 0 if is_asn == false