#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int mod = 1e9 + 7;
const int inf = (1 << 30) - 1;
const ll infll = (1LL << 61) - 1;
#define fast() ios::sync_with_stdio(false), cin.tie(0), cout.tie(0)

int N, ans, one, nine, other;
string s, t = "";

int main()
{
    cin >> N >> s;

    for (int i = 0; i < N; i++)
    {
        if (s[i] == '1')
            one++, t = t + "1";
        else if (s[i] == '9')
            nine++, t = t + "9";
        else
            ans++;
    }

    N = t.size();

    int now_one = 0, now_nine = 0;

    for (int i = 0; i < N; i++)
    {
        if (t[i] == '1')
        {
            now_one++;
        }
        else
        {
            now_nine++;
            if (now_one > 0)
                now_one--, now_nine--, ans++;
        }
    }
    ans += now_one / 2;

    cout << ans << endl;
}