#include <bits/stdc++.h>

#define rep(i,n) for( int i=0; i<n; ++i )
typedef long long ll;
using namespace std;

int main(){
  int n;
  cin >> n;
  string s;
  cin >> s;
  int c[5];
  rep(i,5){c[i]=0;}
  int cnt19 = 0;
  int over9 = 0;
  int cnt991 = 0;
  rep(i,s.length()){
    c[(s[i]-'1')/2]++;
    if ( s[i] == '9' ){
      if ( cnt19 + cnt991 < c[0] ){
        cnt19++;
      } else {
        over9++;
      }
    }
    if ( ( s[i] == '1' ) && ( 1 < over9 ) ){
      over9 -= 2;
      cnt991++;
    }
  }
  cout << c[1]+c[2]+c[3] + cnt19 + cnt991 + (c[0]-cnt19-cnt991)/2 << endl;
}