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 Common Lisp (SBCL 1.1.14) (judge verdict: Accepted)

(defvar *N* nil)
(setf *N* (read))

(defvar *count* *N*)
(defvar *list1* (list nil))
(dotimes (x 10)
  (declare (ignore x))
  (if (= (mod *count* *N*) 0)
      (push *count* *list1*))
  (setq *count* (+ *count* *N*)))

(setq *list1* (cdr (reverse *list1*)))

(setq *count* *N*)
(defvar *list2* (list nil))
(dotimes (x 10)
  (declare (ignore x))
  (when (= (mod *count* 2) 0)
      (push *count* *list2*))
  (setq *count* (+ *count* *N*)))

(setq *list2* (cdr (reverse *list2*)))


(dolist (x *list1*)
  (dolist (y *list2*)
    (if (= x y)
        (progn (format t "~d~%" x)
               (sb-ext:quit)))))