#include <bits/stdc++.h>
using namespace std;

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

int main()
{
    char s[10001];
    int nr, contor = 0;
    fin >> nr;
    fin.ignore();
    fin.getline(s, nr);
    for (int i = 1; i <= nr; i++)
    {
        for(int j = i; j < nr; j++)
            if (s[j] > s[j+1]){
                    swap(s[j],s[j+1]);
                    contor++;
        }
    }

    fout << contor << "\n";
    return 0;
}