#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0;i<n;i++)
using namespace std;
int main() {
    int n; cin >> n;
    string s; cin >> s;
    int ans = 0;
    set<string> seen;
    rep(i, n-1){
        string t = s;
        t[i]='B';t[i+1]='B';
        seen.insert(t);
    }
    cout << seen.size() << endl;
    return 0;
}