#include <bits/stdc++.h>

using namespace std;

const string fisier = "litere";

ifstream fin (fisier + ".in");
ofstream fout (fisier + ".out");

int main(){
  int n; fin >> n;
  string s; fin >> s;
  string t = s;
  sort(t.begin(), t.end());
  map<char, int>mpa, mpb;
  for (int i = 0; i < n; i++){
    mpa[s[i]] += i;
    mpb[t[i]] += i;
  }
  int ans = 0;
  for (char i = 'a'; i <= 'z'; i++){
    ans += abs(mpa[i] - mpb[i]);
  }
  fout << ans - n;
}