#include <iostream>
#include <cstring>
#include <fstream>

using namespace std;

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

int main() {
    int n;
    fin >> n;
    char c[10001];
    for (int i = 0; i < n; i++) {
        fin >> c[i];
    }

    int schimbari = 0;
    for (int i = 0; i < n - 1; i++) {
        for (int j = i + 1; j < n; j++) {
            if (c[i] > c[j]) {

                schimbari++;
            }
        }
    }

    fout << schimbari;
    return 0;
}