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 PHP7 (7.0.15) (judge verdict: Wrong Answer)

<?php
$n = (int)trim(fgets(STDIN));

if ($n === 1) {
    echo 0 . PHP_EOL;
    exit();
}

if ($n % 2 === 0) {
    echo $n . PHP_EOL;
} else {
    echo $n * 2 . PHP_EOL;
}