#include <cmath>
#include <iostream>
#include <string>

int main() {
  int N;
  std::string s;
  std::cin >> N;
  std::cin >> s;
  int cnt1 = 0;
  int ans = 0;
  for (int i = 0; i < N; ++i) {
    if (s[i] == '1') {
      if (cnt1 > 0) {
        ++ans;
        --cnt1;
      } else {
        ++cnt1;
      }
    } else if (s[i] == '9') {
      if (cnt1 > 0) {
        ++ans;
        --cnt1;
      }
    } else {
      ++ans;
    }
  }
  std::cout << ans << std::endl;
}