#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, scnt = 0;
    bool fst = false;
    string s, tmp;
    cin >> n >> s;
    for (int i = 0; i < n-1; i++){
        if (i && s[i-1] == 'B' && s[i] == 'A' && s[i+1] == 'B') continue;
        else if (s[i] == 'B' && s[i+1] == 'B'){
            if(!fst) {
                cnt++;
                fst = true;
            }
            continue;
        }
        cnt++;
    }
    cout << cnt << endl;
}