#include <bits/stdc++.h>
using namespace std;
ifstream fin("litere.in");
ofstream fout("litere.out");
int n;
long long inversiuni;
char v[10001];
int main()
{
  ios_base::sync_with_stdio(false);
  fin>>n;
  for (int i=0;i<n;++i)
  {
    fin>>v[i];
    for (int j=i-1;j>=0;--j)
    {
      if (v[i]<v[j]) inversiuni++;
    }
  }
  fout<<inversiuni<<'\n';
  return 0;
}