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++14 (GCC 5.4.1) (judge verdict: Wrong Answer)

#include <bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (int)(n); i++)
#define F first
#define S second
#define all(x) (x).begin(),(x).end()
using namespace std;
typedef long long ll;
using vi = vector<int>;
using vvi = vector<vi>;
using pii = pair<int,int>;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return 1; } return 0; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return 1; } return 0; }
ll gcd(ll a, ll b) { return b?gcd(b, a%b):a;}
ll lcm(ll a, ll b) { return a*b/gcd(a,b);}
ll MOD=1000000007;

int main(){
  int n;
  string s;
  cin>>n>>s;
  int tmp=0;
  int ans=0;
  rep(i,n){
    if(s.at(i)=='A' && tmp==0){
      tmp++;
      continue;
    }
    if(s.at(i)=='B' && tmp==1){
      tmp++;
      continue;
    }
    if(s.at(i)=='C' && tmp==2){
      ans++;
      tmp=0;
      continue;
    }
    tmp=0;  
  }
  cout<<ans<<endl;
}