#include <iostream>
#include <fstream>
#include <cstring>
using namespace std;

ifstream in("litere.in");
ofstream out("litere.out");

const int dim = 10002;
const int dmax = 30;

char s[dim];

int F[dmax];

int ans;

int N;

int main()
{
    in >> N;

    in.get();
    in.get(s, dim);

    int length = strlen(s);

    for(int i = 0; i < length; i++)
    {
        int ind = (int)(s[i]) - 97 + 1;

        F[ind] += 1;

        for(int j = 1; j <= 26; j++)
            if(j > ind) ans += F[j];
    }

    out << ans;

    return 0;
}