#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  string s;
  cin >> n >> s;
  s = "#" + s + "#";
  for (auto del : "zyxwvutsrqponmlkjihgfedcb") {
    for (int i = 1; i < s.size(); i++) {
      if (s[i] == del && (s[i - 1] + 1 == del || s[i + 1] + 1 == del)) {
        s = s.substr(0, i) + s.substr(i + 1);
        i = 0;
      }
    }
  }
  cout << n + 2 - s.size();
  return 0;
}
