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 (1.42.0) (judge verdict: Accepted)

use proconio::{input, fastout};
use proconio::marker::{Chars};
use proconio::marker::Usize1;
use std::cmp::*;

macro_rules! debug {
      ($($a:expr),*) => {
          eprintln!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
      }
  }
  fn gcd(mut a: usize, mut b: usize) -> usize {
    if a<b {
        let mut tmp = a;
        a = b;
        b = tmp;
    } 
    let mut r = a % b;
    while r!=0 {
        a = b;
        b = r;
        r = a % b;
    }
    b
}

  #[fastout]
fn main() {
    input!{
        n: usize,
    }

    if n%2==0 {
        println!("{}", n);
    } else {
        println!("{}", n*2);
    }

}