#include <fstream>
#include <cstring>

using namespace std;

int N;
char s[10010];
int v[30];

void Citire ()
{
    ifstream fin ("litere.in");
    fin >> N;
    fin >> s;
    fin.close ();
}

int Business ()
{
    memset (v, 0, sizeof (v));
    for (int i = 0; i < N; i++)
    {
        s[i] -= 97;
    }
    int S = 0;
    v[(int) s[0]]++;
    for (int i = 1; i < N; i++)
    {
        for (int j = 30; j > (int) s[i]; j--)
        {
            S += v[j];
        }
        v[(int) s[i]]++;
    }
    return S;
}

void Scriere ()
{
    ofstream fout ("litere.out");
    int a = Business ();
    fout << a;
    fout.close ();
}

int main ()
{
    Citire ();
    Scriere ();
    return 0;
}