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>

int gcd(int a, int b) {
  int tmp;
  if(a < b) { tmp = a; a = b; b = tmp; }
  while(b != 0)
  {
    a %= b;
    tmp = a; a = b; b = tmp;
  }
  return a;
}

int main()
{
  int n; scanf("%d", &n);
  printf("%d\n", n*2/gcd(n, 2));
  return 0;
}