#include <fstream>
using namespace std;

ifstream f("litere.in"); ofstream g("litere.out");

const int NMAX = 10009;
char a[NMAX];
int n, nbr;

inline void read_Data() {

    f>>n;
    f.getline(a, NMAX);
    f.getline(a, NMAX);
}

inline void solve() {

    char aux;

    for(int i = 0; i < n - 1; ++i)  {

        if(a[i] > a[i + 1]) {

            aux = a[i];
            a[i] = a[i + 1];
            a[i + 1] = aux;
            ++nbr;
        }

        for(int j = i; j > 0; --j)
            if(a[j] < a[j - 1]) {

                aux = a[j];
                a[j] = a[j - 1];
                a[j - 1] = aux;
                ++nbr;
            }
            else    break;
    }
}

int main() {

    read_Data();
    solve();

    g << nbr << '\n';


    g.close();
    return 0;
}