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 <inttypes.h>

uint64_t gcd(uint64_t a, uint64_t b) {
	while (b > 0) {
		uint64_t r = a % b;
		a = b;
		b = r;
	}
	return a;
}

uint64_t lcm(uint64_t a, uint64_t b) {
	return a / gcd(a, b) * b;
}

int main(void) {
	uint64_t N;
	if (scanf("%" SCNu64, &N) != 1) return 1;
	printf("%" PRIu64 "\n", lcm(2, N));
	return 0;
}