#include <fstream>
using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");
char s[10001], aux;
int i, n, ct;
bool ok;
int main()
{
    f >> n;
    f.get();
    f >> s;
    do
    {
        ok = 1;
        for(i = 1; i < n; ++ i)
            if(s[i] < s[i - 1])
            {
                aux = s[i];
                s[i] = s[i - 1];
                s[i - 1] = aux;
                ct ++;
                ok = 0;
            }
    }while(ok == 0);
    g << ct;
    return 0;
}