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.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace AtCorder
{
    class Program
    {
        static void Main(string[] args)
        {
            var N = long.Parse(Console.ReadLine());
            var ls = Console.ReadLine().Split(' ').Select(x => long.Parse(x)).ToList();

            if (N == 1)
            {
                Console.WriteLine("0");
                return;
            }


            for (int i = 0; i < ls.Count(); i++)
            {
                ls[i] -= i + 1;
            }

            ls.Sort();
            var ans = ls.Select(x => Math.Abs(x - ls[int.Parse((N / 2).ToString())])).Sum();
            var ansMin = ls.Select(x => Math.Abs(x - ls[int.Parse(((N / 2) - 1).ToString())])).Sum();

            Console.WriteLine((Math.Min(ans, ansMin)).ToString());
        }
    }
}