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: Wrong Answer)

n = gets.to_i
num = gets.strip.split.map(&:to_i)
rec = Hash.new()
for i in 0..n-1
  if rec.key?(num[i])
    rec[num[i]] += 1
  else
    rec[num[i]] = 1
  end
end
a = rec.to_a
a.sort! {|a,b| a[0] <=> b[0]}.reverse!
ary = []
for i in 0..a.size-1
  if a[i][1] >= 4
    2.times do
      ary << a[i][0]
    end
    break
  elsif
    a[i][1] == 2 || a[i][1] == 3
    ary << a[i][0]
    if ary.size == 2
      break
    end
  else
    next
  end
end
if ary.size == 2
  puts ary[0]*ary[1]
else
  puts 0
end