import std;

void main() {
    int N;
    readf("%d\n", N);

    auto S = readln.chomp.to!(dchar[]);

    int[string] list;
    foreach (i; 1 .. N) {
        dchar F = S[i-1], B = S[i];

        S[i-1] = 'B', S[i] = 'B';
        ++list[S.to!string];

        S[i-1] = F, S[i] = B;
    }

    auto res = list.length;
    res.writeln;
}