#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }

const long long MAX = 5100000;
const long long INF = 1LL << 60;
const long long mod = 1000000007LL;
//const long long mod = 998244353LL;

using namespace std;
typedef unsigned long long ull;
typedef long long ll;

int main()
{
	/*
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	*/

	ll N; scanf("%lld", &N);
	string t; cin >> t;
	string s;
	ll res = 0;
	ll cnt1 = 0, cnt9 = 0;

	for (ll i = 0; i < N; i++) {
		if (t[i] != '1' && t[i] != '9') {

			res++;
		}
		else if (t[i] == '1') {
			cnt1++;
		}
		else {
			if (cnt1 > 0) {
				cnt1--;
				res++;
			}
			else cnt9++;
		}
	}
	//cout << res << endl;
	ll mn = min(cnt9 / 2, cnt1);
	cnt9 -= mn * 2;
	cnt1 -= mn;
	res += mn;
	res += cnt1 / 2;
	cout << res << endl;
	return 0;
}