#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)

int dp[200000+1];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int n;
  string s;
  cin >> n >> s;

  vector<int> p1, p9;

  int ret = 0;
  REP (i, n) {
    char c = s[i];
    if (c == '1')
      p1.push_back(i);
    else if (c == '9')
      p9.push_back(i);
    else
      ++ret;
  }

  int match = 0;
  int j = p9.size() - 1;
  for (int i = p1.size() - 1; i >= 0 && j >= 0; i--) {
    if (p1[i] < p9[j]) {
      ++match;
      --j;
    }
  }

  ret += match;
  ret += (p1.size() - match) / 2;
  cout << ret << endl;
  
  return 0;
}