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.strip.to_i
a = gets.strip.split(' ').map(&:to_i)

sticks = {}
a.map do |stick|
  if sticks[stick]
    sticks[stick] += 1
  else
    sticks[stick] = 1
  end
end

# puts sticks
# puts a.uniq.sort.reverse

found = 0
a.uniq.sort.reverse.each do |current|
  count = sticks[current]
  if count >= 4
    # puts "current has more 4"
    if found > 0
      puts current * found
    else
      puts current * current
    end
    exit 0
  elsif count == 2 or count == 3
    # puts "current has 2"
    if found > 0
      # puts "found * current: #{found} * #{current}"
      puts found * current
      exit 0
    else
      # puts "found will be #{current}"
      found = current
    end
  end
end

puts 0