#include <fstream>
using namespace std;
int n,i,aux,sol;
char v[10010],sortat;
ifstream fin ("litere.in");
ofstream fout ("litere.out");


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

    do {
        sortat = 1;/// presupun ca sirul este sortat
        for (i=1;i<n;i++)
            if (v[i] > v[i+1]) {
                aux = v[i];
                v[i] = v[i+1];
                v[i+1] = aux;
                sortat = 0; /// daca la parcurgerea curenta am facut macar o interschimbare sirul nu e sortat deci voi relua

                sol++;

            }
    } while (sortat == 0);
    /*
    for (i=1;i<n;i++)
        for (j=i+1;j<=n;j++)
            if (v[i] > v[j]) {
                aux = v[i];
                v[i] = v[j];
                v[j] = aux;
            }
    */
    fout<<sol;
}