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: Accepted)

#include<iostream>
#include<algorithm>
#include<vector>
#include<stack>
#include <cmath>
#include <limits>
#include<set>
#include <iomanip>
#include <queue>
#include <map>
#include <string>
#pragma GCC optimize("Ofast")
using namespace std;
typedef long long ll;
typedef double ld;
const long long INF=(1LL<<62);
const double inf=pow(10,10);
double pi=3.141592653589793;
const int dx[4]={0,1,0,-1};
const int dy[4]={1,0,-1,0};
const int ddx[8]={1,0,-1,-1,-1,0,1,1};
const int ddy[8]={1,1,1,0,-1,-1,-1,0};
const ll MOD = 4000007;
void init(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
}

std::vector<bool> IsPrime;

void sieve(size_t max){
    if(max+1 > IsPrime.size()){ 
        IsPrime.resize(max+1,true); 
    } 
    IsPrime[0] = false;
    IsPrime[1] = false;

    for(size_t i=2; i*i<=max; ++i)
        if(IsPrime[i])
            for(size_t j=2; i*j<=max; ++j) 
                IsPrime[i*j] = false;     
}

int main(){
	init();
	ll a;cin>>a;
	string s;cin>>s;
	ll n=0;
	for(int i=0;i+2<s.size();i++){
		if(s[i]=='A'&&s[i+1]=='B'&&s[i+2]=='C')n++;
	}
	cout<<n<<endl;
}