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)

#define _CRT_SECURE_NO_WARNINGS
#define lp(i,n) for(int i=0;i<n;i++)
#define atcoder(x)int TAKAHASIKUN[x] 
#include<bits/stdc++.h>

using namespace std;
int ieei(int x,int y) {
	if (x % y == 0)
		return y;
	else
		return ieei(y, x%y);
}
int main() {
	int n;
	cin >> n;

	if (n < 2)
		cout << n * 2 / ieei(2, n) << endl;
	else
		cout << n * 2 / ieei(n, 2) << endl;

	return 0;

}