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 2.0.3) (judge verdict: Wrong Answer)

(defun make-acceptor (string)
  (let ((num 0)
        (pos 0))
  (lambda (c)
    (if (null c)
        num
        (cond ((and (= pos (1- (length string))) (char= c (char string pos)))
               (incf num)
               (setf pos 0))
              ((char= c (char string pos))
               (incf pos))
              (t
               (setf pos 0)))))))

(let ((n (read))
      (x (make-acceptor "ABC")))
  (loop :for i :from 1 :to n
        :for c := (read-char)
        :do (funcall x c))
  (format t "~A~%"  (funcall x nil)))