#include<bits/stdc++.h>
using namespace std;
int main () {
    int N;
    cin >> N;
    string s;
    cin >> s;
    s = "B" + s + "B";
    int ans = 0;
    for (int i = 0; i <= N; i ++) {
        if (s[i] == 'A' || s[i + 1] == 'A') {
            ans ++;
        }
    }
    for (int i = 0; i < N; i ++) {
        if (s.substr(i, 3) == "BAB") {
            ans --;
        }
    }
    cout << ans << endl;
}