// #define DEBUGGING
#include <bits/stdc++.h>
using namespace std;
#define endl '\n'
#define ALL(V) (V).begin(), (V).end()
#define ALLR(V) (V).rbegin(), (V).rend()

template <typename T> using V = vector<T>;
template <typename T> using VV = V<V<T>>;
using ll = int64_t;
using ull = uint64_t;
using PLL = pair<ll, ll>;

template <typename T> const T& var_min(const T &t) { return t; }
template <typename T> const T& var_max(const T &t) { return t; }
template <typename T, typename... Tail> const T& var_min(const T &t, const Tail&... tail) { return min(t, var_min(tail...)); }
template <typename T, typename... Tail> const T& var_max(const T &t, const Tail&... tail) { return max(t, var_max(tail...)); }
template <typename T, typename... Tail> void chmin(T &t, const Tail&... tail) { t = var_min(t, tail...); }
template <typename T, typename... Tail> void chmax(T &t, const Tail&... tail) { t = var_max(t, tail...); }
template <typename T> const T& clamp(const T &t, const T &low, const T &high) { return max(low, min(high, t)); }
template <typename T> void chclamp(T &t, const T &low, const T &high) { t = clamp(t, low, high); }

namespace init__ {

struct InitIO {
    InitIO() {
        cin.tie(nullptr);
        ios_base::sync_with_stdio(false);
        cout << fixed << setprecision(30);
    }
} init_io;

}

#ifdef DEBUGGING
// #include "../debug/debug.cpp"
#include "../../debug/debug.cpp"
#else
#define DEBUG(...) 0
#define DEBUG_SEPARATOR_LINE 0
#endif

template <typename T>
T make_v(T init) { return init; }

template <typename T, typename... Tail>
auto make_v(T init, size_t s, Tail... tail) {
#define rec make_v(init, tail...)
    return V<decltype(rec)>(s, rec);
#undef rec
}

const ll inf = 5e15;

int main() {
    ll N;
    cin >> N;
    ll ans = 0;
    queue<ll> one, nine;
    for(ll i = 0; i < N; i++) {
        char a;
        cin >> a;
        if(a == '1') one.push(i);
        else if(a == '9') nine.push(i);
        else ans++;
    }
    one.push(inf);
    nine.push(inf);
    ll ocnt = 0, ncnt = 0;
    while(1 < one.size() || 1 < nine.size()) {
        if(one.front() < nine.front()) {
            one.pop();
            ocnt++;
            if(2 <= ocnt) {
                ans++;
                ocnt -= 2;
            } else if(2 <= ncnt) {
                ocnt--;
                ncnt -= 2;
                ans++;
            }
        } else {
            nine.pop();
            ncnt++;
            if(ocnt) {
                ocnt--;
                ncnt--;
                ans++;
            }
        }
    }
    cout << ans << endl;
    return 0;
}