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 Rust (1.15.1) (judge verdict: Accepted)

fn gcd(a: u64, b: u64) -> u64 { if b == 0 { a } else { gcd(b, a % b) } }
fn lcm(a: u64, b: u64) -> u64 { a / gcd(a, b) * b }


fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let mut input: Vec<i32> = s.split_whitespace().map(|x| x.parse::<i32>().unwrap()).collect();
    let n = input[0];

    let ans = lcm(n as u64, 2);
    println!("{}", ans);
}