#include <bits/stdc++.h>
using namespace std;
int main() {
  long long n, i, ans, m, j, k;
  string s;
  cin >> n >> s;
  ans = 0;
  char ch;
  for (i = 25; i >= 0; i--) {
    ch = i + 'a';
    for (j = 1; j < (long long)s.size(); j++) {
      if (s[j] == ch and s[j - 1] + 1 == ch) {
        s.erase(s.begin() + j);
        ans++;
        j--;
      }
    }
    for (j = 0; j < (long long)s.size() - 1; j++) {
      if (s[j] == ch and s[j + 1] + 1 == ch) {
        s.erase(s.begin() + j);
        ans++;
        j -= 2;
      }
    }
  }
  cout << ans;
  return 0;
}
