#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    int N, ans=0;
    bool f=0;
    string S;
    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 (!f){
                ans++;
                f=1;
            }
            continue;
        }
        ans++;
    }

    cout << ans << endl;

    return 0;
}