#include <bits/stdc++.h>
using namespace std;

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int N;
    cin >> N;
    string S;
    cin >> S;
    int counter = 0;
    int ans = 0;
    for (char s : S){
        if (s == '1'){
            ++counter;
        }else if (s == '9'){
            if (counter > 0){
                --counter;
                ++ans;
            }
        }else{
            ++ans;
        }
    }
    cout << ans + counter / 2 << endl;
    return 0;
}