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: Accepted)

using System;
using System.Collections.Generic;
using System.Linq;

namespace CountABC
{
    class Program
    {
        static void Main(string[] args)
        {
            int lettersAmount = int.Parse(Console.ReadLine());
            List<char> lettersInput = Console.ReadLine().ToList();

            List<string> abcSentences = new List<string>();

            int abcAmount = 0;
            for(int i = 0; i < lettersAmount; i++)
            {
                string abcString = "";

                if (lettersInput[i].ToString() == "A" && i < lettersAmount && i + 1 < lettersAmount && i + 2 < lettersAmount)
                {
                    abcString += lettersInput[i].ToString() + lettersInput[i + 1].ToString() + lettersInput[i + 2].ToString();
                }

                if(abcString == "ABC")
                {
                    abcAmount++;
                }
            }
            Console.WriteLine(abcAmount);     
        }
    }
}