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 Haskell (GHC 7.10.3) (judge verdict: Wrong Answer)

main = do 
  n <- getLine 
  s <- getLine
  print $ countABC 0 s

countABC :: Int -> String -> Int
countABC c [] = c
countABC c (x:xs) | x == 'A'  = countB c xs
                  | otherwise = countABC c xs 

countB c []                 = c
countB c (x:xs) | x == 'B'  = countC c xs
                | otherwise = countABC c xs

countC c []                 = c 
countC c (x:xs) | x == 'C'  = countABC (c+1) xs
                | otherwise = countABC c xs