#include <bits/stdc++.h>
#define LOCAL

using namespace std;

using ll = long long;
// const int mod = 998244353;
// const int mod = 1000000000 + 7;

#define mem(a, b) memset(a, b, sizeof(a))
#define REP(i, a) for (int i = 0; i < a; ++i)
#define FOR(i, a, b) for (int i = a; i < b; ++i)
#define ALL(a) a.begin(), a.end()

inline void quickread() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    cout << fixed << setprecision(10);
}

inline void print_vector(vector<int> &A){
    for (auto&& x : A){
        cout << x << " ";
    }
    cout << endl;
}

inline void print_vector(vector<ll> &A){
    for (auto&& x : A){
        cout << x << " ";
    }
    cout << endl;
}

inline void print_array(const int A[], int n) {
    REP(i, n) {
        if (i < n - 1) {
            cout << A[i] << " ";
        } else {
            cout << A[i] << endl;
        }
    }
}

ll gcd(ll x, ll y) {
    return (y == 0 ? x : gcd(y, x % y));
}
ll lcm(ll x, ll y) {
    return x * y / gcd(x, y);
}

#ifdef LOCAL
#define trace(...) __f(#__VA_ARGS__, __VA_ARGS__)
#else
#define trace(...) 42
#endif
template <typename Arg1>
void __f(const char* name, Arg1&& arg1){
  cerr << name << ": " << arg1 << endl;
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args){
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << ": " << arg1 << " |";
  __f(comma + 1, args...);
}

vector<int> prime{1};

void solve() {
    int n;
    cin >> n;
    string s;
    cin >> s;

    int res = 0;

    int cur = 0;
    char pre = ' ';
    bool start = true;
    bool find = false;
    bool has_b = false;
    for (auto c : s) {
        if (c == 'A') {
            if (pre == 'A') cur++;
            else cur = 1;

            pre = 'A';
        } else {
            if (pre == 'A') {
                if (start) {
                    res += cur;
                } else {
                    if (cur == 1) res++;
                    else res += (cur + 1);
                }
            }
            if (pre == 'B') {
                find = true;
            }
            pre = 'B';
            cur = 0;
            start = false;
            has_b = true;
        }
    }

    if (!has_b) {
        cout << n - 1 << endl;
        return;
    }

    res += cur;

    cout << res + find << endl;
}

int main() {
    quickread();

    int t = 1;
    // bool multi = false;
    // if (multi) cin >> t;
    // else t = 1;

    for (int _ = 0; _ < t; _++) {
        solve();
    }

    return 0;
}