Problem:
Score : 200 points

Problem Statement

We have a permutation p = {p_1,\ p_2,\ ...,\ p_n} of {1,\ 2,\ ...,\ n}.

Print the number of elements p_i (1 < i < n) that satisfy the following condition:

p_i is the second smallest number among the three numbers p_{i - 1}, p_i, and p_{i + 1}.

Constraints

All values in input are integers.

3 \leq n \leq 20

p is a permutation of {1,\ 2,\ ...,\ n}.

Input

Input is given from Standard Input in the following format:

n
p_1 p_2 ... p_n

Output

Print the number of elements p_i (1 < i < n) that satisfy the condition.

Sample Input 1

5
1 3 5 4 2

Sample Output 1

2

p_2 = 3 is the second smallest number among p_1 = 1, p_2 = 3, and p_3 = 5. Also, p_4 = 4 is the second smallest number among p_3 = 5, p_4 = 4, and p_5 = 2. These two elements satisfy the condition.

Sample Input 2

9
9 6 3 2 5 8 7 4 1

Sample Output 2

5

Solution in Common Lisp (SBCL 2.0.3) (judge verdict: Accepted)

(defun solve(a &optional (ans 0))
    (cond
      ((<= (length a) 2) ans)
      (t
       (when
	   (or (< (first a) (second a) (third a))
	       (> (first a) (second a) (third a)))
	 (incf ans))
       (solve (rest a) ans))))

(defun main()
  (let ((n (read))
	(a (read-from-string (concatenate 'string "(" (read-line) ")"))))
    (princ (solve a))
    (fresh-line)))

(main)