#include <bits/stdc++.h>
#define rep(i, n) for(int(i) = 0; (i) < (n); (i)++)
#define FOR(i, m, n) for(int(i) = (m); (i) < (n); (i)++)
#define ALL(v) (v).begin(), (v).end()
#define LLA(v) (v).rbegin(), (v).rend()
#define PB push_back
#define MP(a, b) make_pair((a), (b))
using namespace std;
template <class T> inline vector<T> make_vec(size_t a, T val) {
    return vector<T>(a, val);
}
template <class... Ts> inline auto make_vec(size_t a, Ts... ts) {
    return vector<decltype(make_vec(ts...))>(a, make_vec(ts...));
}
template <typename T> inline T read() {
    T t;
    cin >> t;
    return t;
}
template <typename T> inline vector<T> readv(size_t sz) {
    vector<T> ret(sz);
    rep(i, sz) cin >> ret[i];
    return ret;
}
template <typename... Ts> inline tuple<Ts...> reads() {
    return {read<Ts>()...};
}
template <typename T> struct edge {
    int to;
    T cost;
    edge(int t, T c) : to(t), cost(c) {}
};
using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using Graph = vector<vector<int>>;
template <typename T> using WGraph = vector<vector<edge<T>>>;
const int INF = 1 << 30;
const ll LINF = 1LL << 60;
const int MOD = 1e9 + 7;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int N = read<int>();
    string s = read<string>();
    string t = "";
    int res = 0;
    rep(i, N) {
        if(s[i] == '1' || s[i] == '9') {
            t += s[i];
        } else {
            res++;
        }
    }
    stack<char> st;
    rep(i, t.size()) {
        if(t[i] == '9' && !st.empty() && st.top() == '1') {
            st.pop();
            res++;
        } else {
            st.push(t[i]);
        }
    }
    int cnt1 = 0, cnt9 = 0;
    while(!st.empty()) {
        if(st.top() == '1')
            cnt1++;
        else
            cnt9++;
        st.pop();
    }
    cout << res + max(cnt1 / 2, min(cnt1, cnt9 / 2)) << endl;
}