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 static System.Math;

class Program{
    static void Main(){
        int med = 0;
        int sorrow = 0;
        int N = int.Parse(Console.ReadLine());
        string[] S = Console.ReadLine().Split(' ');
        int[] A = new int[N];
        int[] B = new int[N];
        for(int i = 0; i < N; i++){
            A[i] = int.Parse(S[i]);
            B[i] = A[i] - (i+1);
        }

        Array.Sort(B);
        if(N % 2 == 1){
            med = B[N/2];
        }
        else{
            med = (B[N/2-1] + B[N/2])/2;
        }

        for(int j = 0; j < N; j++){
            sorrow += Abs(B[j] - med);
        }
        Console.WriteLine(sorrow);
    }
}