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

int main() {
    int n;
    string s;
    cin >> n >> s;
    set<string> res;
    for (int i = 0; i < n - 1; i++) {
        string t = s;
        t[i] = 'B';
        t[i + 1] = 'B';
        res.insert(t);
    }
    cout << res.size() << endl;
    return 0;
}