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>
#include <vector>
#include <queue>
#include <set>
#include <cmath>
#include <stack>
#include <string>
#include <deque>
#include <map>
#include <algorithm>

using namespace std;
//--------------------
int gcd(int a, int b) {
    return b == 0 ? a : gcd(b, a % b);
}

//------------
void func() {
    int N;
    cin >> N;
    if (N % 2 == 0) {
        cout << N << endl;
    } else {
        cout << (N << 1) / gcd(2,N) << endl;
    }
}

int main() {
    func();
    return 0;
}