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++14 (GCC 5.4.1) (judge verdict: Accepted)

#include <iostream>
#define xl unsigned long long
using namespace std;
int n;
xl mcd(xl a,xl b){
    while(a!=0 && b!=0){
        if(a>b)a=a%b;
        else b%=a;
    }
    if(a==0)return b;
    else return a;
}
xl mcm(xl x){
    xl aux;
    if(x>2){
        aux=x/mcd(x,2);
        return 2*aux;
    }
    else{
         aux=2/mcd(x,2);
         return x*aux;
    }
    return 0;
}
int main(){
    cin>>n;
    cout<<mcm(n);
return 0;
}