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>
//大小比較(大)
long long int big(long long int a, long long int b) {
	if (a >= b) {
		return a;
	}
	else {
		return b;
	}
}

//大小比較(小)
long long int small(long long int a, long long int b) {
	if (a >= b) {
		return b;
	}
	else {
		return a;
	}
}

main() {
	long long int n, m,k;
	scanf("%lld", &n);

	if (n % 2 == 0) { printf("%lld", n); }
	else { printf("%lld", 2 * n); }
}