#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using PII = pair<ll, ll>;
#define FOR(i, a, n) for (ll i = (ll)a; i < (ll)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
template<typename T> void chmin(T &a, const T &b) { a = min(a, b); }
template<typename T> void chmax(T &a, const T &b) { a = max(a, b); }
struct FastIO {FastIO() { cin.tie(0); ios::sync_with_stdio(0); }}fastiofastio;
#ifdef DEBUG_ 
#include "../program_contest_library/memo/dump.hpp"
#else
#define dump(...)
#endif
const ll INF = 1LL<<60;

int main(void) {
    ll n;
    string s;
    cin >> n >> s;

    // 3 5 7
    ll ret = 0;
    string t = "";
    REP(i, n) {
        if(s[i]=='1' || s[i]=='9') t += s[i];
        else {
            ret++;
        }
    }

    dump(t);

    // 19
    n = t.size();
    vector<bool> del(n);
    stack<ll> st;
    REP(i, n) {
        if(t[i]=='1') st.push(i); 
        else {
            if(st.size()>0) {
                del[st.top()] = true; st.pop();
                del[i] = true;
                ret++;
            }
        }
    }
    s = "";
    REP(i, n) if(!del[i]) s += t[i];
    n = s.size();

    dump(s);

    // 991
    while(st.size()) st.pop();
    del.assign(n, false);
    REP(i, n) {
        if(s[i]=='9') {
            st.push(i);
        } else {
            if(st.size()>=2) {
                del[st.top()] = true; st.pop();
                del[st.top()] = true; st.pop();
                del[i] = true;
                ret++;
            }
        }
    }
    t = "";
    REP(i, n) if(!del[i]) t += s[i];
    n = t.size();

    dump(t);

    ll cnt1 = 0;
    REP(i, n) if(t[i]=='1') cnt1++;

    ret += cnt1 / 2;

    cout << ret << endl;

    return 0;
}