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 Python (3.4.3) (judge verdict: Accepted)

#最大公約数
def gcd(a, b):
    while b != 0:
        a, b = b, a % b
    return a

#最大公約数の個数
def ngcd(a):
    res = a[0]
    for i in range(len(a)):
        if res != 1:
            res = gcd(a[i], res)
    return res

#最小公倍数
def lcm(a,b):
    return a * b // gcd(a, b)

#最小公倍数の個数
def nlcm(a):
    res = a[0]
    for i in range(len(a)):
        res = lcm(res, a[i])
    return res

n = int(input())
print(lcm(n, 2))