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.to_i
A=gets.split.map(&:to_i)
h=Hash.new{0}
A.each{|a|
    h[a]+=1
}
h.reject!{|k,v|v<2}
e=[]
h.each_key{|k|
    e<<k
    if h[k]>=4
        e<<k
    end
}
e.sort!
if e.size>=2
    puts e[-1]*e[-2]
else
    puts 0
end