#include <bits/stdc++.h>
#include<iostream>
#include<map>
#include<vector>
#include <algorithm>
#include<math.h>
#include <iomanip>
#include<set>
#include <numeric>
#include<string>
using ll = long long;
using namespace std;

int main()
{
    ll n, cnt = 0;
    string s, tmp;
    cin >> n >> s;
    for (int i = 0; i < n-1; i++){
        tmp = s.substr(i, 3);
        if (tmp == "BAB") cnt++;
        else if (tmp == "BBA" && s[i+3] == 'B') cnt++;
        else if (i >= 1 && tmp == "ABB" && s[i-1] == 'B') cnt++;
    }
    cout << s.size() - 1 - cnt << endl;
}