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)

use std::io::stdin;
fn get_string() -> String {
    let mut s = String::new();
    stdin().read_line(&mut s).unwrap();
    s.trim().to_string()
}

macro_rules! input {
    ($single:ty) => ( get_string().parse::<$single>().unwrap() );
    ($plural:ty,) => ({
        let line = get_string();
        line.split_whitespace().map(|v| v.parse::<$plural>().unwrap()).collect::<Vec<$plural>>()
    });
    ($($plural:ty),+) => ({
        let line = get_string();
        let mut iter = line.split_whitespace();
        ($(iter.next().unwrap().parse::<$plural>().unwrap()),+)
    });
    ($single:ty; $times:expr) => ( (0..$times).map(|_| input!($single)).collect::<Vec<$single>>() );
    ($($plural:ty),+; $times:expr) => ( (0..$times).map(|_| input!($($plural),+)).collect::<Vec<($($plural),+)>>() );
}

#[allow(dead_code)]
fn get_value<T: std::str::FromStr>() -> T {
    get_string().parse().ok().unwrap()
}
#[allow(dead_code)]
fn get_values_for<T: std::str::FromStr>(times: u64) -> Vec<T> {
    (0..times).map(|_| get_value()).collect()
}
#[allow(dead_code)]
fn get_vector<T: std::str::FromStr>() -> Vec<T> {
    get_string()
        .split_whitespace()
        .map(|v| v.parse().ok().unwrap())
        .collect()
}
#[allow(dead_code)]
fn get_vectors_for<T: std::str::FromStr>(times: u64) -> Vec<Vec<T>> {
    (0..times).map(|_| get_vector()).collect()
}

fn main() {
    let n = input!(u32);
    if n % 2 == 1 {
        println!("{}", n * 2);
    } else {
        println!("{}", n);
    }
}