#include <bits/stdc++.h>
using namespace std::literals::string_literals;
using i64 = std::int_fast64_t;
using std::cout;
using std::endl;
using std::cin;

template<typename T>
std::vector<T> make_v(size_t a){return std::vector<T>(a);}

template<typename T,typename... Ts>
auto make_v(size_t a,Ts... ts){
  return std::vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...));
}

int main() {
	int n; scanf("%d", &n);
	std::string s; cin >> s;

	std::vector<int> cnt(10, 0);
	for(int i = 0; i < s.size(); i++) cnt[s[i] - '0']++;
	int ans = cnt[3] + cnt[5] + cnt[7];

	int tmp = 0;
	for(int i = 0; i < s.size(); i++) {
		if(s[i] == '1') tmp++;
		if(tmp and s[i] == '9') {
			tmp--;
			ans++;
		}
	}
	ans += tmp >> 1;
	
	printf("%d\n", ans);
	return 0;
}