Problem:
Score : 100 points

Problem Statement

You are given a positive integer N.
Find the minimum positive integer divisible by both 2 and N.

Constraints

1 \leq N \leq 10^9

All values in input are integers.

Input

Input is given from Standard Input in the following format:

N

Output

Print the minimum positive integer divisible by both 2 and N.

Sample Input 1

3

Sample Output 1

6

6 is divisible by both 2 and 3.
Also, there is no positive integer less than 6 that is divisible by both 2 and 3.
Thus, the answer is 6.

Sample Input 2

10

Sample Output 2

10

Sample Input 3

999999999

Sample Output 3

1999999998

Solution in Ruby (2.3.3) (judge verdict: Runtime Error)

N = gets.to_i
a = gets.split.map(&:to_i)
sum = 0
for i in 0..a.length-1
  a[i] = a[i] - (i+1)
  sum += a[i]
end
a = a.sort

def bad(a,b)
  sum = 0
  for i in 0..a.length-1
    sum += (a[i]-b).abs
  end
  sum
end

if N==1
  puts a[0]
else
  puts [bad(a,a[(N-1)/2]),bad(a,a[(N-1)/2+1])].min
end