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: Time Limit Exceeded)

a = gets.to_i
b = gets.split(" ").map(&:to_i).sort
c=[]
d=[]
for num in 1..b[-1] do
  if b.count(num) >= 4
    c << num
  elsif b.count(num) >=2
    d << num
  else
  end  
end  
e = c.reverse
f = d.reverse
if e == [] && f == []
  puts 0
elsif e[0] == f[0]
  puts e[0]**2
else
  puts f[0]*f[1]
end