#include <iostream>
#include <string>
#include <vector>

//1, 3, 5, 7, 11, 19, 991

int main() {                                                        int N;                                                            std::string s;                                                    std::vector<int> a;                                               std::cin >> N;                                                    std::cin >> s;                                                    int ans = 0;
                                                                    for (int i = 0; i < N; ++i) {
    if (s[i] != '9' && s[i] != '1') {
      ++ans;
    } else {
      a.push_back(s[i] - '0');
    }
  }

  // 11, 19, 991
  // 99999911111111111
  int cnt1 = 0, cnt9 = 0;
  for (int i = 0; i < a.size(); ++i) {
    if (a[i] == 9 && cnt1 > 0) {
      --cnt1;
      ++ans;
    } else if (a[i] == 9) {
      ++cnt9;
    } else if (a[i] == 1) {
      ++cnt1;
    }
  }
  int cnt991 = std::min(cnt9 / 2, cnt1);
  cnt9 -= cnt991 * 2;
  cnt1 -= cnt991;
  ans += cnt991 + cnt1 / 2;
  std::cout << ans << std::endl;
}