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;

namespace ABC150
{
	class Program
	{
		static void Main(string[] args)
		{
			int n = int.Parse(Console.ReadLine());
			string s = Console.ReadLine();

			string word = "ABC";
			int counter = 0;
			int index = s.IndexOf(word);
			int next;

			if(index >= 0)
			{
				counter++;

				while (true)
				{
					next = index + word.Length;

					if (next < s.Length)
					{
						index = s.IndexOf(word, next);

						if(index < next)
						{
							break;
						}

						counter++;
					}
					else
					{
						break;
					}
				}
			}

			Console.WriteLine(counter);
		}
	}
}