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 Haskell (GHC 7.10.3) (judge verdict: Accepted)

import Control.Applicative

main = do
    ns <- map read.words <$> getLine
    putStrLn.show $ answer ns

answer [n] = last . filter (\v -> mod v n == 0 && mod v 2 == 0) $ [2*n,2*n-(max n 2)..max n 2]