#include<iostream>
#include<string>
#include<set>
using namespace std;

int main() {
    int n;
    string s;
    cin >> n >> s;
    int res = 0;
    bool b = false;
    for (int i = 0; i < n - 1; i++) {
        if (b == false && s[i] == 'B' && s[i + 1] == 'B') {
            b = true;
            res++;
        }
        else if (s[i] == 'B' && s[i + 1] == 'B') continue;
        else if (i != 0 && s[i - 1] == 'B' && s[i] == 'A' && s[i + 1] == 'B') continue;
        else res++;
    }
    cout << res << endl;
    return 0;
}