#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);
  
  
  do {
      sortat = 1;
      for (int i = 0; i < strlen (s) - 1; i++)
       if (s[i] > s[i + 1])
       {
           swap (s[i], s[i + 1]);
           sortat = 0;
           cnt++;
       }
  } while (sortat == 0);
   
   cout << cnt;
   
    return 0;
}