#include <iostream>
#include <vector>
#include <deque>
using namespace std;

int main(){
    int N;
    string S,T = "";
    cin >> N >> S;
    int ans = 0;
    for(int i=0;i<N;i++){
        if(S[i]!='1' && S[i]!='9') ans++;
        else T += S[i];       
    }
    int ans2 = 0;
    int n = T.size();
    vector<int> used(n,0);
    deque<int> nine;
    for(int i=0;i<n;i++){
        if(T[i]=='9') nine.push_back(i);
        else{
            if(nine.size()>=2){
                used[i] = 1;
                for(int j=0;j<2;j++){
                    used[nine.front()] = 1;
                    nine.pop_front();
                }
                ans++;
            }
        }
    }
    int ni = 0,one = 0;
    for(int i=n-1;i>=0;i--){
        if(used[i]) continue;
        if(T[i]=='9') ni++;
        else{
            if(ni){
                ni--;
                ans++;
            }else one++;
        }
    }
    cout << ans+one/2 << endl;
}