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: Accepted)

import Data.List
import Data.Maybe

findString :: (Eq a) => [a] -> [a] -> Maybe Int
findString search str = findIndex (isPrefixOf search) (tails str)

sol s
    | isNothing i = 0
    | otherwise   = 1 + (sol $ drop (fromJust i + 3) s)
    where
        i = findString "ABC" s

main=do
    _ <- getLine
    s <- getLine
    print $ sol s