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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;

namespace a
{
    class Program
    {
        static void Main(string[] args)
        {
            var n = long.Parse(Console.ReadLine());
            Console.WriteLine(Lcm(2,n));
        }

        //最小公倍数
        static long Lcm(long m, long n){
        	return (m * n) / Gcd(m, n);
        }

        //最大公約数
        static long Gcd(long m, long n)
        {
	        while (m % n != 0){
        		var temp = n;
		        n = m % n;
		        m = temp;
	        }
        	return n;
        }
    }
}