#include <fstream>
#include <cstring>

using namespace std;

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

int main() 
{
    int n;
    fin >> n;
    fin.ignore();

    char s[10001];
    fin >> s;

    bool sortat;
    int count = 0;

    do {
        sortat = false;
        for (int i = 0; i < n - 1; i++)
            if (s[i] > s[i + 1]) {
                char aux;
                aux = s[i];
                s[i] = s[i + 1];
                s[i + 1] = aux;
                
                count ++;
                sortat = true;
            }
    } while (sortat);

    fout << count;

    return 0;
}