#include <fstream>
using namespace std;

int main() {
    ifstream fin("litere.in");
    ofstream fout("litere.out");

    int n;
    char s[10005];
    fin >> n >> s;

    long long rez = 0;
    for (int i = 0; i < n - 1; i++)
        for (int j = i + 1; j < n; j++)
            if (s[i] > s[j])
                rez++;

    fout << rez;
    return 0;
}