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

mt19937 rnd(chrono::steady_clock::now().time_since_epoch().count());

struct MillerRabin {
    int modpow(int a, int n, int mod) {
        if (n == 0) return 1;
        if (n % 2 == 0) {
            int t = modpow(a, n / 2, mod);
            return t * t % mod;
        }
        return a * modpow(a, n - 1, mod) % mod;
    }

    int modinv(int n, int mod) { return modpow(n, mod - 2, mod); }

    bool is_prime(int n, int k = 50) {
        if (n == 2) return true;
        if (n < 2 || n % 2 == 0) return false;
        int d = n - 1;
        while (d % 2 == 0) {
            d /= 2;
        }
        for (int i = 0; i < k; i++) {
            int a = rnd() % (n - 2) + 1;
            int t = d;
            int y = modpow(a, t, n);
            while (t != n - 1 && y != 1 && y != n - 1) {
                y = modpow(y, 2, n);
                t *= 2;
            }
            if (y != n - 1 && t % 2 == 0) {
                return false;
            }
        }
        return true;
    }
} mr;

signed 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 kyu = 0;
    int ichi = 0;
    // 19
    for (int i = (int)t.size() - 1; i >= 0; i--) {
        if (t[i] == '9') {
            kyu++;
        } else {
            if (kyu) {
                ans++;
                kyu--;
            } else {
                ichi++;
            }
        }
    }

    // 991
    ans += min(kyu / 2, ichi);

    cout << ans << endl;
}