#include<iostream>
#include<string>
#include<iomanip>
#include<cmath>
#include<vector>
#include<algorithm>
#include<stack>

using namespace std;

#define int long long
#define endl "\n"

const long long INF = (long long)1e18;
const long long MOD = 1'000'000'007; 

string yn(bool f){return f?"Yes":"No";}
string YN(bool f){return f?"YES":"NO";}




signed main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	cout<<fixed<<setprecision(10);
	
	int N, con = 0;
	string S;
	int con1 = 0, con9 = 0;
	vector<int> hoge, fuga, x;
	
	cin>>N;
	cin>>S;
	
	con1 = count(S.begin(), S.end(), '1');

	for(int i = 0; i < S.size(); i++){
		// cout<<"i = "<<i<<" "<<con1<<" "<<con9<<" "<<con<<" S = "<<S[i]<<endl;
		if(S[i] == '1') {
			x.push_back(1);
		} else if(S[i] == '9'){
			if(x.size() && x.back() == 1){
				x.pop_back();
				con++;
				con1--;
			} else {
				x.push_back(9);
			}
		} else {
			con++;
		}
	}
	
	int a = 0, b = 0;
	for(int i = 0; i < x.size(); i++){
		if(x[i] == 1){
			if(b >= 2){
				b -= 2;
				con++;
				con1--;
			} else {
				a++;
			}
		} else {
			b++;
		}
	}
	
	con += con1/2;
	
	cout<<con<<endl;
	
	return 0;
}