#include <fstream>
#include <cstring>

using namespace std;

const int NMAX = 10000;
char sir[1 + NMAX];

int main()
{
    ifstream in("litere.in");
    ofstream out("litere.out");
    int n;
    bool ok = false;
    int nr = 0;

    in >> n;

    in >> sir;
    while (!ok)
    {
        ok = true;
        for (int i = 0; i < n - 1; i++)
        {
            if (sir[i] > sir[i + 1])
            {
                swap(sir[i], sir[i + 1]);
                ok = false;
                nr++;
            }
        }
    }

    out << nr << '\n';

    return 0;
}