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: Time Limit Exceeded)

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp12
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.ReadLine();
            var str = Console.ReadLine();
            int cnt = 0;
            int s = 0;


            while (true)
            {
                s = str.IndexOf("ABC", s);
                if (s == -1) break;
                cnt++;
            }
            Console.WriteLine(cnt);
        }

        static void MainA(string[] args)
        {
            var arr = Console.ReadLine().Split(' ').Select(x => int.Parse(x)).ToArray();
            Console.WriteLine(arr[0] * 500 >= arr[1] ? "Yes" : "No");
        }
    }
}