#include <fstream>

using namespace std;
char v[10100];
char c;
int n, i, ok, sol;

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]) {
                c = v[i];
                v[i] = v[i+1];
                v[i+1] = c;
                ok = 0;
                sol++;
            }
    } while (ok == 0);
    fout<<sol;
    return 0;
}