#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<ll, ll> P;
#define rep(i, n) for(ll (i) = 0; (i) < (n); (i)++)
#define rep1(i, n) for(ll (i) = 1; (i) <= (n); (i)++)
#define rrep(i, n) for(ll (i) = (n) - 1; (i) >= 0; (i)--)
#define rrep1(i, n) for(ll (i) = (n); (i) >= 1; (i)--)
const ll INF = 1145141919;
const ll MOD = 1000000007;
template<class T> void chmax(T &a, const T &b){if(a < b){a = b;}}
template<class T> void chmin(T &a, const T &b){if(a > b){a = b;}}

int main(){

    ll N;
    cin >> N;
    string s;
    cin >> s;
    
    ll ans = 0;
    priority_queue<ll>nine_q;
    priority_queue<ll, vector<ll>, greater<ll> >one_q;
    nine_q.push(-1);
    one_q.push(N);
    rep(i, N){
        if(s[i] == '1')one_q.push(i);
        if(s[i] == '3')ans++;
        if(s[i] == '5')ans++;
        if(s[i] == '7')ans++;
        if(s[i] == '9')nine_q.push(i);
    }
    while(one_q.top() < nine_q.top()){
        s[one_q.top()] = '0';
        s[nine_q.top()] = '0';
        one_q.pop();
        nine_q.pop();
        ans++;
    }

    ll one = 0, nine = 0;
    rep(i, N){
        if(s[i] == '9')nine++;
        if(s[i] == '1'){
            if(nine >= 2){
                nine-=2;
                ans++;
            }
            else one++;
        }
    }
    cout << ans + one / 2 << endl;

    return 0;
}