#include <fstream>
#define nmax 10005
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");

int main()
{
    int n, numbering = 0;
    char c[nmax];
    fin >> n;
    for (int i = 1; i <= n; ++i)
        fin >> c[i];
    while (true) {
        int partial_numbering = 0;
        for (int i = 2; i <= n; ++i) {
            if (c[i] < c[i - 1]) {
                char aux = c[i - 1];
                c[i - 1] = c[i];
                c[i] = aux;
                ++partial_numbering;
            }
        }
        if (partial_numbering == 0) {
            fout << numbering;
            return 0;
        }
        numbering += partial_numbering;
    }
}