#include <fstream>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n,i,s,sortat;
char v[260],aux;
int main () {
    fin>>n;
    for (i=1;i<=n;i++) {
        fin>>v[i];
    }
    do {
        sortat=1;
        for (i=1;i<=n-1;i++) {
            if (v[i]>v[i+1]) {
                aux=v[i+1];
                v[i+1]=v[i];
                v[i]=aux;
                sortat=0;
                s++;
            }
        }

    }while (sortat==0);

    fout<<s;
}