#include <iostream>
#include <fstream>
#include <string>
#include <cmath>

using namespace std;

int ap[30],rez;
string x;

int main()
{
    int n;
    ifstream f("litere.in");
    ofstream g("litere.out");
    f>>n>>x;
    for(int i=0;i<x.size();++i){

        ++ap[x[i]-'a'];
        int tmp = 0;
        for(char p='z';p>x[i];--p)
            tmp+=ap[ p - 'a' ];
        rez+= tmp;
    }
    g<<rez;
    return 0;
}