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
c = gets.split.to_a
h = {}
n.times do |i|
  if h[c[i].to_i]
    h[c[i].to_i] += 1
  else
    h[c[i].to_i] = 1
  end
end
s = h.select{|k, v| v >= 4}.keys.sort{|a, b| b<=>a}
t = h.select{|k, v| v >= 2}.keys.sort{|a, b| b<=>a}
ans = 0
if s.size > 0
  ans = s[0] * s[0]
end
if t.size > 1
  ans = t[0] * t[1] if ans < t[0] * t[1]
end
puts ans