#include <fstream>

using namespace std;

int n,i,nr,ok;

char v[10001],f[10001],aux;

ifstream fin ("litere.in");

ofstream fout ("litere.out");

int main (){

    fin>>n;
    for (i=1;i<=n;i++){
        fin>>v[i];

    }
    do {
        ok = 1;
        for (i=1;i<n;i++)
            if (v[i] > v[i+1]) {
                aux = v[i];
                v[i] = v[i+1];
                v[i+1] = aux;
                nr++;
                ok = 0;
            }
    } while (ok == 0);
    fout<<nr;
    return 0;
}