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 (2.7.1) (judge verdict: Accepted)

n = gets.chomp.to_i
a = gets.chomp.split(" ").map(&:to_i).sort
hash = Hash.new(0)
a.each do |i|
    hash[i] += 1
end
hash = hash.to_a
arr = []
while true
    point = hash.pop
    if point[1] >= 2 && point[1] <= 3
        arr << point[0]
    elsif point[1] >= 4
        arr << point[0]
        arr << point[0]
    end
    if hash == []
        break
    end
end
ans = 1
if arr.size >= 2
    2.times do |i|
        ans *= arr.shift
    end
    puts ans
else
    puts "0"
end