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: Time Limit Exceeded)

#include<iostream> 
#include<vector>
#include<algorithm>
using namespace std ;
#define rep(i,n) for( int i = 0 ; i < n ; i++ )
typedef long long ll ;

int main(){
    ll n ;
    cin >> n ;
    rep(i,1999999998){
        if((i+1) % 2 == 0 && (i+1) %n == 0 ){
            cout << i+1 << endl;
            return 0 ;
        }
    } 
}