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.Linq;
using System.Collections.Generic;
class Program
{
	static void Main(string[] args)
	{
	    int n = IO.GetInt();
	    string s = IO.GetString();
	    int count = 0;
	    int index = 0;
	    while(index < n){
	        if(s.IndexOf("ABC",index)>=0){
	            count++;
	            index = s.IndexOf("ABC",index);
	            index++;
	        }else{
	            break;
	        }
	    }
	    Console.WriteLine(count);
	}

}

static class IO
{
    static public string GetString() { return Console.ReadLine(); }
    static public int GetInt() { return int.Parse(Console.ReadLine()); }
    static public long GetLong() { return long.Parse(Console.ReadLine()); }
    static public List<string> GetStringList() { return Console.ReadLine().Split(' ').ToList(); }
    static public List<int> GetIntList() { return Console.ReadLine().Split(' ').Select(int.Parse).ToList(); }
    static public List<long> GetLongList() { return Console.ReadLine().Split(' ').Select(long.Parse).ToList(); }
    static public List<double> GetDoubleList() { return Console.ReadLine().Split(' ').Select(double.Parse).ToList(); }
    static public void WriteStrings<T>(IEnumerable<T> values) { foreach (var o in values) { Console.Write(o + " "); } }
}