#include<iostream>
#include<vector>
#include<algorithm>
using namespace std;
typedef long long ll;
typedef pair<ll,ll> P;
signed main(){
  ll n,cnt=0,one_c=0;
  string s;
  cin >> n;
  cin >> s;
  for(int i=0;i<n;i++){
    if(s[i]=='1'){
      one_c++;
    }else if(s[i]!='9'){
      cnt++;
    }
  }
  cout << cnt + one_c/2<<endl;
}