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>
#include<stdlib.h>
#include<string.h>
#include<math.h>

#define MAX(p,q) ((p>q)?(p):(q))
#define MIN(p,q) ((p<q)?(p):(q))

#define REP(i,n) for(i=0;i<n;i++)

int gcd(int a,int b);

int main(void)
{
  int n;
  scanf("%d",&n);
  int ans;
  ans = (n%2==0)? n:n*2;
  printf("%d",ans);
  return 0;
}

int gcd(int a,int b)
{
  int max,min,tmp;
  max = MAX(a,b);
  min = MIN(a,b);
  if(max%min==0) return min;
  else
  {
    tmp = min;
    min = max%min;
    max = tmp;
    return gcd(max,min);
  }
}