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 Ruby (2.3.3) (judge verdict: Accepted)

N = gets.chomp.to_i
S = gets.chomp
f = 0
answer = 0
for i in 0...N do
    if f == 0
        if S[i] == "A"
            f += 1
        else
            f = 0
        end
    elsif f == 1
        if S[i] == "B"
            f += 1
        elsif S[i] == "A"
            f = 1
        else
            f = 0
        end
    elsif f == 2
        if S[i] == "A"
            f = 1
        else
            f = 0
        end
        if S[i] == "C"
            answer += 1
        end
    end
end
puts answer