#include <fstream>
#include <cstring>
using namespace std;

ifstream fout ("litere.in");
ofstream fout ("litere.out");

int main() {
    int n;
    fin >> n;
    char s[1005];
    fin >> s;
    long long inversiuni = 0;

    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (s[i] > s[j])
                inversiuni++;
        }
    }

    fout << inversiuni << endl;
    return 0;
}