#include <bits/stdc++.h>

using namespace std;

char s[10001];
int n, cnt, sortat;

int main()
{
    ifstream cin ("litere.in");
    ofstream cout ("litere.out");
    
    cin >> n;
    cin.get();
    cin.get (s, 10001);
  
  
  for (int i = 0; i < (strlen (s) - 1); i++)
   for (int j = i + 1; j < strlen (s); j++)
    if (s[i] > s[j]) cnt++;
   
   cout << cnt;
   
    return 0;
}