#include<bits/stdc++.h>
using namespace std;
int main () {
    int N;
    cin >> N;
    string s;
    cin >> s;
    set<pair<int, int>> st;
    for (int i = 0; i < N - 1; i ++) {
        int a = -1, b = -1;
        if (s[i] == 'A') {
            a = i;
        }
        if (s[i + 1] == 'A') {
            b = i + 1;
        }
        if (a == -1) {
            swap(a, b);
        }
        st.emplace(a, b);
    }
    cout << st.size() << endl;
}