#include<fstream>
using namespace std;
ifstream f("litere.in");
ofstream g("litere.out");
unsigned int n, V[30], k;
void citire()
{
    char a;
    f>>n;
    for(int i=1; i<=n; ++i)
    {
        f>>a;
        V[a-96]++;
        for(int j=a-95; j<=26; ++j)
            k+=V[j];
    }
}
int main()
{
    citire();
    g<<k<<'\n';
    g.close();
    return 0;
}