#include <bits/stdc++.h>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
const int nmax = 10001;
char s[nmax];
int sol, n;
void read()
{
    fin >> n;
    fin.get();
    fin.getline(s, nmax);
    fin.close();
}
void bubble_sort()
{
    for(int i = 0; i < n - 1; ++i)
    {
        bool ok = false;
        for(int j = 0; j < n - i - 1; j++)
            if(s[j] > s[j + 1])
            {
                swap(s[j], s[j + 1]);
                ok = true;
                sol++;
            }
        if(!ok)
            break;
    }
    fout << sol;
}
int main()
{
    read();
    bubble_sort();
    return 0;
}