#include <iostream>
#include <iomanip>
#include <cstring>
#include <algorithm> 
#include <math.h>
#include <queue>
#include <functional>
#include <map>
#include <vector>
#include <string>
#include <set> 
using namespace std;

typedef long long ll;
typedef pair<ll, int> P;
typedef pair<pair<int, int>, int> PP;

int dx[4] = { 1,0,-1,0 };
int dy[4] = { 0,1,0,-1 };

const ll INF = 1e15;
const int MAX = 510000;
const ll MOD = 1000000007;


int main(void) {
	int N; cin >> N;
	string S; cin >> S;
	int ichi = 0, kyu = 0, ans = 0;
	for (int i = 0; i < N; i++) {
		if (S[i] == '1') ichi++;
		else if (S[i] == '9') {
			kyu++;
			if (ichi > 0) {
				ans++; ichi--; kyu--;
			}
		}
		else ans++;
	}
	ans += min(ichi, kyu / 2); ichi -= min(ichi, kyu / 2);
	ans += ichi / 2;

	cout << ans << endl;
}