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 input<T: std::str::FromStr>() -> T {
    let stdin = std::io::stdin();
    let s: String = std::io::Read::bytes(stdin.lock()).by_ref()
        .map(|c| c.unwrap() as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    s.parse::<T>().ok().expect("error")
}

fn main() {
    let n: u32 = input();
    println!("{}",
        if n % 2 == 0 {
            n
        } else {
            n * 2
        }
    );
}