#include <iostream>
#include <fstream>

using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");

int main (){

    int n;
    fin >> n;
    string sir;
    fin >> sir;
    int rez = 0;
    for (int i = 0; i < sir.size(); i++)
    {
        for (int j = 0; j < i; j ++){
            if(sir[i] < sir[j]){
                rez++;
            }
        }
    }
    fout << rez;
}