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 C# (Mono 4.6.2.0) (judge verdict: Wrong Answer)

using System;
class Program {
    static int n = 0;
    static bool[] flg = new bool[3];

    static void Main (string[] args) {
        var inp = Console.ReadLine().Split(' ');
        var inp2 = Console.ReadLine().Split(' ');

        for(int i = 0;i < int.Parse(inp[0]);i++) {
            a(inp2[0][i]);
        }

        Console.WriteLine(n);
    }

    static void a (char str) {
        if(!flg[0]) {
            if(str.Equals('A')) {
                flg[0] = true;
            } else {
                ini();
            }

            return;
        }

        if(!flg[1]) {
            if(str.Equals('B')) {
                flg[1] = true;
            } else {
                ini();
            }

            return;
        }

        if(!flg[2]) {
            if(str.Equals('C')) {
                flg[2] = true;
                n++;
            }
            ini();

            return;
        }
    }

    static void ini () {
        for(int i = 0;i < 3;i++) {
            flg[i] = false;
        }
    }
}