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)

n = gets.to_i
A = gets.split().map(&:to_i)
B = A.uniq.sort.reverse

C = B.map do |b|
  [b, A.count(b)]
end

# p H.to_h
C.select! do |c|
  c[1] >= 2
end

if C != []
  rec = C[0][0]*C[1][0]
else
  rec = 0
end

D = C.select {|c| c[1] >= 4}
if D != []
  sq = D[0][0]**2
else
  sq = 0
end

# p rec
# p sq
p [rec,sq].max