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)

#![allow(unused_imports)]
#![allow(dead_code)]
use std::io::{stdin, stdout, stderr, Write, BufWriter, BufReader, BufRead};

macro_rules! read_from_line {
    ($inbuf:ident => $($name:ident : $ty:ty),* ) => {
        let mut buf = String::new();
        $inbuf.read_line(&mut buf).unwrap();
        buf.pop();
        let mut words = buf.split_whitespace();
        $(
            let $name:$ty = words.next().unwrap().parse().unwrap();
        )*
    };
}

fn main() {
    let cout = stdout();
    let mut cout = BufWriter::new(cout.lock());
    let cin = stdin();
    let mut cin = BufReader::new(cin.lock());

    //read_from_line!(cin => a:i32, b:String);
    //let xs: Vec<i32> = strio::read_many_from_line(&mut cin);
    
    read_from_line!(cin => n:i32);
    if n % 2 == 0 {
        writeln!(cout, "{}", n).unwrap();
    } else {
        writeln!(cout, "{}", n * 2).unwrap();
    }

}

mod strio {
    use std::str::FromStr;
    use std;

    pub fn read_from_line<T, R> (r: &mut R) -> T where
        T: FromStr,
        <T as std::str::FromStr>::Err : std::fmt::Debug,
        R: std::io::BufRead,
    {
        let mut buf = String::new();
        r.read_line(&mut buf).unwrap();
        buf.pop();
        buf.parse().unwrap()
    }

    pub fn read_many_from_line<T, R> (r: &mut R) -> Vec<T> where
        T: FromStr,
        <T as std::str::FromStr>::Err : std::fmt::Debug,
        R: std::io::BufRead,
    {
        let mut buf = String::new();
        r.read_line(&mut buf).unwrap();
        buf.pop();
        buf.split_whitespace().map(|x| x.parse().unwrap()).collect()
    }
}