#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<long long,long long> pll;
#define pb push_back
#define mp make_pair
#define rep(i,n) for(int i=0;i<(n);++i)
constexpr int mod=1000000007;
constexpr int mod1=998244353;
vector<int> dx={0,1,0,-1},dy={-1,0,1,0};
bool inside(int y,int x,int h,int w){
	if(y<h && y>=0 && x<w && x>=0) return true;
	return false;
}





int main(){
	cin.tie(0);
	ios::sync_with_stdio(false);
	int n;cin >> n;
	string s;cin >> s;
	int ans = 0, cnt = 0, cnt1 = 0;
	rep(i,n){
		if(s.at(i) == '1'){
			cnt++;
		}
		else if(s.at(i) == '9'){
			if(cnt){
				ans++;
				cnt--;
			}
			else cnt1++;
		}
		else ans++;
	}
	int mi = min(cnt, cnt1 / 2);
	ans += mi;
	cnt -= mi;
	ans += cnt / 2;
	cout << ans << endl;
}