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.to_i
line = gets
data = line.split(" ")
data.map!{|i| i.to_i}
data.sort!{|a, b| b <=> a}
two = -1
area = 0
(N-1).times do |i|
  #p "two=#{two} data[i]=#{data[i]} data[i+1]=#{data[i+1]}"
  if two != -1
    if !data[i].equal?(two) and data[i].equal?(data[i+1])
      area = two * data[i]
      break
    end
  elsif i <= (N-4)
    if data[i].equal?(data[i+3])
      area = data[i] * data[i]
      break
    elsif data[i].equal?(data[i+1])
      two = data[i]
    end
  end
end
p area