#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;
	
	cin>>N;
	cin>>S;

	
	for(int i = 0; i < N; i++){
		if(S[i] == '1') {
			if(con9 >= 2){
				con9 -= 2;
				con++;
			} else {
				con1++;
			}
		} else if(S[i] == '9'){
			if(con1 >= 1){
				con1--;
				con++;
			} else {
				con9++;
			}
		} else {
			con++;
		}
	}
	
	con += con1/2;
	
	cout<<con<<endl;
	
	return 0;
}