#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using Graph = vector<vector<int>>;
vector<int> x{31,28,31,30,31,30,31,31,30,31,30,31};
int main() {
    int N; cin >> N;
    string S; cin >> S;
    set<string> X;
    for(int i = 0; i < N - 1; i++) {
        string s = S;
        s[i] = 'B';
        s[i + 1] = 'B';
        X.insert(s);
    }
    cout << X.size() << endl;
}