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: Wrong Answer)

using System;
using static System.Console;
using static System.Math;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        long N = long.Parse(ReadLine());

        List<long> prime = PrimeFactors(N).ToList();
        prime.RemoveAll(item => item == 2);

        long result = 1;
        for (int i = 0; i < prime.Count; i++)
        {
            result *= prime[i];
        }

        WriteLine(result*2);
    }
    public static IEnumerable<long> PrimeFactors(long n)
    {
        long i = 2;
        long tmp = n;

        while (i * i <= n) 
        {
            if (tmp % i == 0)
            {
                tmp /= i;
                yield return i;
            }
            else
            {
                i++;
            }
        }
        if (tmp != 1) yield return tmp;
    }
}