#include <iostream>
#include <algorithm>
#include <string>
#include <vector>
#include <cmath>
#include <map>
#include <queue>
#include <iomanip>
#include <set>
#include <tuple>
#define mkp make_pair
#define mkt make_tuple
#define rep(i,n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
const ll MOD=1e9+7;

int main(){
  int N;
  cin>>N;
  string S;
  cin>>S;

  int ans=0;
  string T="";
  for(int i=0;i<N;i++){
    if(S[i]=='1'||S[i]=='9') T+=S[i];
    else ans++;
  }

  int one=0,nine=0;
  for(int i=T.size()-1;i>=0;i--){
    if(T[i]=='9') nine++;
    else{
      if(nine>0){
        nine--;
        ans++;
      }else one++;
    }
  }

  if(one>0){
    int q=min(nine/2,one);
    ans+=q;
    one-=q;
  }

  ans+=one/2;
  cout<<ans<<endl;


  return 0;
}