Problem:
Score : 200 points

Problem Statement

We have a string S of length N consisting of uppercase English letters.

How many times does ABC occur in S as contiguous subsequences (see Sample Inputs and Outputs)?

Constraints

3 \leq N \leq 50

S consists of uppercase English letters.

Input

Input is given from Standard Input in the following format:

N
S

Output

Print number of occurrences of ABC in S as contiguous subsequences.

Sample Input 1

10
ZABCDBABCQ

Sample Output 1

2

Two contiguous subsequences of S are equal to ABC: the 2-nd through 4-th characters, and the 7-th through 9-th characters.

Sample Input 2

19
THREEONEFOURONEFIVE

Sample Output 2

0

No contiguous subsequences of S are equal to ABC.

Sample Input 3

33
ABCCABCBABCCABACBCBBABCBCBCBCABCB

Sample Output 3

5

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

(defun check_A (x)
  (when (and x (char= (car x) #\A))
			 (check_B (cdr x))))
(defun check_B (x)
  (when (and x (char= (car x) #\B))
			 (check_C (cdr x))))
(defun check_C (x)
  (and x (char= (car x) #\C)))

(defun cnt (x)
  (if x
	(+ (if (check_A x) 1 0) (cnt (cdr x)))
	0))

(defparameter n (read))
(let ((str (concatenate 'list (read-line))))
  (princ (cnt str)))