#include "bits/stdc++.h"

using namespace std;
#ifdef _DEBUG
#define _GLIBCXX_DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

#define int long long
#define ll long long
#define DBG 1
#define rep(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define loop(n) rep(loop, (0), (n))
#define all(c) begin(c), end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)(1e9) + 7;
#define fi first
#define se second
#define pb push_back
#define eb emplace_back
using pii = pair<int, int>;
// template<class T> ostream &operator<<(ostream &os,T &t){dump(t);return os;}
template <typename T, typename S>istream &operator>>(istream &is, pair<T, S> &p) { is >> p.first >> p.second; return is; }
//template <typename T, typename S>ostream &operator<<(ostream &os, pair<T, S> &p) {os << p.first << " " << p.second;return os;}

template <typename T> void printvv(const vector<vector<T>> &v) {
	cerr << endl;
	rep(i, 0, v.size()) rep(j, 0, v[i].size()) {
		if (typeid(v[i][j]).name() == typeid(INF).name() and v[i][j] == INF) {
			cerr << "INF";
		}
		else
			cerr << v[i][j];
		cerr << (j == v[i].size() - 1 ? '\n' : ' ');
	}
	cerr << endl;
}

#ifndef _DEBUG
#define printvv(...)
#endif
void YES(bool f) { cout << (f ? "YES" : "NO") << endl; }
void Yes(bool f) { cout << (f ? "Yes" : "No") << endl; }
template <class T, class U>bool chmin(T& a, U b) { if (a > b) { a = b; return true; }return false; }
template <class T, class U>bool chmax(T& a, U b) { if (a < b) { a = b; return true; }return false; }
bool is_prime(int x) {
	if (x <= 1)
		return false;
	else if (x == 2)
		return true;
	if (x % 2 == 0)
		return false;
	for (int i = 3; i * i <= x; i += 2)
		if (x % i == 0)
			return false;
	return true;
}
signed main(signed argc, char *argv[]) {
	cin.tie(0);
	ios::sync_with_stdio(false);
	cout << fixed << setprecision(12);

	//vector<int>x = { 1,9 };
	//vector<int>p;
	//loop(5) {
	//	vector<int>y;
	//	for (auto a : x) {
	//		y.eb(10 * a + 1);
	//		y.eb(10 * a + 9);
	//	}
	//	x.clear();
	//	for (auto b : y) {
	//		if (is_prime(b)) {
	//			p.eb(b);
	//		}
	//		else {
	//			x.pb(b);
	//		}
	//	}
	//}
	//dump(p);
	//dump(x);

	int N; cin >> N;
	string s; cin >> s;

	int ans = 0;
	ans += count(all(s), '3');
	ans += count(all(s), '5');
	ans += count(all(s), '7');

	int a = 0, b = 0;
	int cnt = 0;
	rrep(i, 0, s.size()) {
		if (s[i] == '9') {
			b++;
		}
		else if (s[i] == '1') {
			if (b > 0) {
				cnt++;
				b--;
			}
			else {
				a++;
			}
		}
	}
	ans += cnt;

	while (b >= 2 and a >= 1) {
		ans++;
		b -= 2;
		a -= 1;
	}

	ans += a / 2;

	cout << ans << endl;

	return 0;
}