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 PHP (5.6.30) (judge verdict: Accepted)

<?php
//最大公約数
function gcd($m, $n){
    if($n > $m) list($m, $n) = array($n, $m);

    while($n !== 0){
        $tmp_n = $n;
        $n = $m % $n;
        $m = $tmp_n;
    }
    return $m;
}

//最小公倍数
function lcm($m, $n){
    return $m * $n / gcd($m, $n);
}

echo lcm(2, trim(fgets(STDIN)))."\n";