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;
class Program{
  static void Main(string[] args){
    int n = int.Parse(Console.ReadLine());
    int ans = 0;
    string s = Console.ReadLine();
    while (s.Length > 0) {
      if (s.Length > 2) {
        if (s.StartsWith("ABC")) {
          s = s.Substring(3);
          ans++;
        } else {
          s = s.Substring(1);
        }
      } else {
        s = "";
      }
    }
    Console.WriteLine(ans);
  }
}