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: Runtime Error)

n=gets.to_i
m=gets.split.map(&:to_i)
square=[]
rectangle=[]
number=[]
result=[]
count=Array.new(n+1,0)
for i in 0..m.length-1
if number.index(m[i])
    count[m[i]]+=1
    if count[m[i]]==1
    rectangle<<m[i]
    end
else
number<<(m[i])
end


if count[m[i]]==3
    square<<count[m[i]]
end

end



rectangle.sort!

if rectangle.length>=2
result<<rectangle[-1]*rectangle[-2]
end

if square[0]!=nil
    result<<square.max**2
end

if result[0]!=nil
    puts result.max
else
  puts 0
end