#include<bits/stdc++.h>
using namespace std;

#define rep(i,n) for(ll i=0;i<(n);++i)
#define reps(i,n) for(ll i=1;i<=(n);++i)
using ll = long long;
constexpr long long INF = (1LL<<60);
constexpr long long MOD = (1e9+7);
template<class T>inline bool chmax(T &a,const T &b){if(a<b){a=b;return true;}return false;}
template<class T>inline bool chmin(T &a,const T &b){if(a>b){a=b;return true;}return false;}
inline void dump(){cout<<endl;}
template<class Head,class... Tail>inline void dump(Head&& head, Tail&&... tail){cout<<head<<", ";dump(forward<Tail>(tail)...);}
template<typename T>inline istream &operator>>(istream&input,vector<T>&v){for(auto &elemnt:v)input>>elemnt;return input;}
template<class T>vector<T> make_vector(size_t a){return vector<T>(a);}
template<class T, class... Ts>auto make_vector(size_t a, Ts... ts){return vector<decltype(make_vector<T>(ts...))>(a, make_vector<T>(ts...));}

main(){
  cin.tie(0);
  ios::sync_with_stdio(0);
  cout<<fixed<<setprecision(10);

  ll n;
  string s;
  cin>>n>>s;
  
  vector<bool> use(n,true);
  ll ans=0;
  rep(i,n){
    if(s[i]=='3'||s[i]=='5'||s[i]=='7'){
      use[i]=false;
      ans++;
    }
  }
  
  string t;
  rep(i,n)if(use[i])t+=s[i];
  n=t.size();
  use.clear();
  use.resize(n,true);
  queue<ll> one;
  rep(i,n){
    if(t[i]=='1'){
      one.emplace(i);
    }
    else if(t[i]=='9'){
      if(one.empty())continue;
      ll idx = one.front();
      one.pop();
      use[idx]=false;
      use[i]=false;
      ans++;
    }
  }

  string r;
  rep(i,n)if(use[i])r+=t[i];
  n=r.size();
  use.clear();
  use.resize(n,true);
  queue<ll> nine;
  rep(i,n){
    if(r[i]=='9'){
      nine.emplace(i);
    }
    else if(r[i]=='1'){
      if(nine.size()<2)continue;
      use[nine.front()]=false;
      nine.pop();
      use[nine.front()]=false;
      nine.pop();
      use[i]=false;
      ans++;
    }
  }

  string str;
  rep(i,n)if(use[i])str+=r[i];
  n=str.size();
  ll cnt=0;
  rep(i,n)if(str[i]=='1')cnt++;
  ans+=cnt/2;
  
  cout<<(ans)<<endl;

}