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)

{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE BangPatterns #-}

import Control.Applicative
import Control.Monad
import Control.Arrow
import Data.List
import Data.Maybe
import Data.Char
import qualified Data.ByteString.Char8 as B
import Text.Printf

readInt = ( readLn :: IO Int )
readInts = map ( read :: String -> Int ) . words <$> getLine

getList = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

main = do
	n <- readInt
	print $ if n `mod` 2 == 0 then n else 2 * n