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
arr = gets.split(" ").map{ |v|
	v.to_i
}

arr.sort!.reverse!

e1 = -1
for i in 0..arr.length-1 do
	if arr[i] == arr[i+1] then
		e1 = arr[i]
		arr.delete_at(i)
		arr.delete_at(i)
		break
	end
end

if e1 < 0 then
	puts 0
	exit
end

e2 = -1
for i in 0..arr.length-1 do
	if arr[i] == arr[i+1] then
		e2 = arr[i]
		arr.delete_at(i)
		arr.delete_at(i)
		break
	end
end

if e2 < 0 then
	puts 0
	exit
end

puts e1 * e2