#include <bits/stdc++.h>
#define ll long long
using namespace std;
#define all(v) v.begin(), v.end()
#define rep(i,n) for (long long i=0;i<(long long)(n);i++)

int main() {
    int N;
    string S;
    cin >> N >> S;
    set<string> ans;
    rep(i,N-1){
        string temp=S;
        temp[i] = 'B';
        temp[i+1] = 'B';
        ans.insert(temp);
    }
    cout << ans.size() << endl;
}