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 (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>

//求最大公约数
int gcd(int a, int b) {
	return b == 0 ? a : gcd(b, a % b);
}


int main()
{
	int n = 0;
	scanf("%d",&n);
	//最小公倍数是两数乘积除以最大公约数
	int s = n * 2 / gcd(n, 2);
	printf("%d", s);

	return 0;
}