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: Runtime Error)

using System;
using System.Linq;
namespace Myatcoder
{
    public class Program
    {
        public static void Main()
        {
            int n = int.Parse(Console.ReadLine());
            int[] A = Console.ReadLine().Split().Select(x => int.Parse(x)).ToArray();

            for (int i = 0; i < n; i++) {
                A[i] = A[i] - i - 1;
            }
            Array.Sort(A);
            long b = (n % 2 == 0 || n == 1 ? A[n / 2] : (A[n / 2] + A[n / 2 - 1]) / 2);

            long ans = 0;
            for (int i = 0; i < n; i++)
            {
                ans += Math.Abs(A[i] - b);
            }
            Console.WriteLine(ans);
        }
    }
}