#include <bits/stdc++.h>
using namespace std;
constexpr int INF = 2e9;
int main() {
  int t;
  t = 1;
  while (t--) {
    int n;
    string s;
    cin >> n;
    cin >> s;
    int res = 0;
    for (int d = 25; d >= 0; d--) {
      string tmp = "";
      for (int i = 0; i < s.size(); i++) {
        int now = s[i] - 'a';
        if (now != d) {
          tmp += s[i];
        } else {
          if (tmp.back() - 'a' == d - 1) {
            res++;
          } else {
            tmp += s[i];
          }
        }
      }
      swap(s, tmp);
      tmp = "";
      for (int i = s.size() - 1; i >= 0; i--) {
        int now = s[i] - 'a';
        if (now != d) {
          tmp += s[i];
        } else {
          if (tmp.back() - 'a' == d - 1) {
            res++;
          } else {
            tmp += s[i];
          }
        }
      }
      reverse(tmp.begin(), tmp.end());
      swap(s, tmp);
    }
    cout << res << endl;
  }
  return 0;
}
