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

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n;
    cin >> n;
    string s;
    cin >> s;

    string t;

    int ans = 0;
    int one = 0, nine = 0;
    for (char c : s) {
        if (!(c == '1' || c == '9')) {
            ans++;
        } else {
            t += c;
        }
    }

    int cur = 0;
    int hoge = 0;
    for (int i = (int)t.size() - 1; i >= 0; i--) {
        if (s[i] == '9')
            cur++;
        else {
            if (cur) {
                ans++;
                cur--;
            } else {
                hoge++;
                if (hoge == 2) {
                    ans++;
                    hoge -= 2;
                }
            }
        }
    }

    cout << ans << endl;
}