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

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

int main()
{
    int n, nr = 0;
    char s[10001];

    fin >> n;
    fin >> s;

    bool sortat = false;

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

    fout << nr;
    return 0;
}