#include <iostream>
#include <fstream>
#include <cstring>

using namespace std;

int A[30], S, N;
char s[10001];

void citire(){

    ifstream f("litere.in");

    f >> N >> s;

    f.close();
}

void rezolva(){

    for ( int i = 0; i < N; i++ ){

        for ( int j = s[i] - 97; j <= 26 ; j++ )
            S += A[j];

        A[s[i] - 96]++;
    }
}

void afis(){

    ofstream g("litere.out");

    g << S << "\n";

    g.close();
}

int main(){

    citire();
    rezolva();
    afis();

    return 0;
}