#include <bits/stdc++.h>
using namespace std;

#ifdef _RUTHEN
#include "debug.hpp"
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    int N;
    cin >> N;
    string S;
    cin >> S;
    int bbcnt = 0;
    rep(i, N - 1) {
        if (S.substr(i, 2) == "BB") {
            bbcnt++;
        }
    }
    int ans = N - 1 - max(0, bbcnt - 1);
    rep(i, N - 2) {
        if (S.substr(i, 3) == "BAB") {
            ans--;
        }
    }
    cout << ans << '\n';
    return 0;
}