#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int,int> pii;

typedef int _loop_int;
#define REP(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG2(x,y) cout<<#x<<": "<<x<<" "<<#y<<": "<<y<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

int main() {
    ios::sync_with_stdio(false); cin.tie(0);
    int n;
    cin>>n;

    string s;
    //string tmp;
    queue<char> q;
    int ans = 0;
    REP(i,n){
        char c;
        cin>>c;
        if(c=='3'||c=='5'||c=='7'){
            ans++;
            continue;
        }
        s += c;
    }
    if(s==""){
        cout << ans << endl;
        return 0;
    }
    
    string ss="";
    bool found19=false;
    do{
        found19=false;
        ss=s[0];
        FOR(i,1,s.size()){
            ss += s[i];
            if(ss[ss.size()-2]=='1' && ss[ss.size()-1]=='9'){
                found19=true;
                ss = ss.substr(0,ss.size()-2);
                ans++;
            }
        }
        s=ss;
    }while(found19);

    int cnt1=0;
    int cnt9=0;
    REP(i,s.size()){
        if(s[i]=='1') cnt1++;
        if(s[i]=='9') cnt9++;
    }

    //DEBUG2(cnt1,cnt9);

    string tmp ="";
    FORR(i,1,s.size()){
        if(s[i]!='1') continue;

        tmp ="";
        FORR(j,0,i){
            if(s[j]=='9'){
                if(tmp.size()==2){
                    ans+=1;
                    cnt1-=1;
                    cnt9-=2;
                    tmp="";
                    break;
                }
                else
                    tmp+="9";
            }   
        }

        if(cnt9<2) break;
    }

    //DEBUG2(cnt1,cnt9);
    
    ans += cnt1/2;

    cout << ans << endl;
    return 0;
}