#include <iostream>
#include <string>
#include <algorithm>
#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <iomanip>
#include <cmath>
#include <stdio.h>
#include <queue>
#include <deque>
#include <cstdio>
#include <set>
#include <map>
#include <bitset>
#include <stack>
#include <cctype>
using namespace std;
int main() {
	int n;
	string s;
	cin >> n >> s;
	int ans = 0;
	int co = 0, co1 = 0;
	for (int i = n - 1; i >= 0; i--) {
		if (s[i] != '1' && s[i] != '9') {
			ans++;
		}
		else if (s[i] == '9') {
			co++;
		}
		else {
			if (co != 0) {
				co--;
				ans++;
			}
			else {
				co1++;
			}
		}
	}
	ans += min(co / 4, co1);
	co1 -= min(co / 4, co1);
	cout << ans + co1 / 2 << endl;
}