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 AtCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            int N = int.Parse(Console.ReadLine());
            string S = Console.ReadLine();

            int ans = 0;
            for(int i = 0; i < N-2; i++)
            {
                if(S[i] == 'A')
                {
                    if (S[i + 1] == 'B')
                    {
                        if(S[i+2] == 'C')
                        {
                            ans++;
                        }
                    }
                }
            }

            Console.WriteLine(ans);
        }
       
    }
}
/*
long a, b, c;
a = long.Parse(Console.ReadLine()); //標準入力
string[] str = Console.ReadLine().Split(' ');//2つ以上のスペース区切り入力の取得
b = long.Parse(str[0]);  //数値で受け取りたい場合は変換する
c = long.Parse(str[1]);
string S = Console.ReadLine();
char[] C = new char[N];
C = S.ToCharArray();
Console.Write("改行なし a = {0} b = {1} c = {2}", a, b, c)//改行なし出力
Console.WriteLine("改行あり a = {0} b = {1} c = {2}", a, b, c);//改行付き出力
Member = ReadLine().Split(' ').Select(long.Parse).ToArray();

string[] str = Console.ReadLine().Split(' ');
long[] a = new long[N];
for(long i = 0; i < N; i++) a[i] = long.Parse(str[i]);
 */
/*
      static long func(long n)
      {
          long d = 0;
          for (long i = 0; i < 10; i++)
          {
              if (n / longPow(10, i) == 0)
              {
                  d = i;
                  break;
              }
          }
          long ret = A * n + B * d;
          return ret;
      }
      static long longPow(long a, long n)
      {
          long b = 1;
          for (long i = 0; i < n; i++) b = b * a;
          return b;
      }
      */