//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <unordered_map>
#include <climits>
#include <set>
#include <unordered_set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>
#include <random>
#include <complex>
#include <regex>
#include <locale>
#include <random>
#include <type_traits>

using namespace std;

#define SHOW_VECTOR(v) {std::cerr << #v << "\t:";for(const auto& xxx : v){std::cerr << xxx << " ";}std::cerr << "\n";}
#define SHOW_MAP(v){std::cerr << #v << endl; for(const auto& xxx: v){std::cerr << xxx.first << " " << xxx.second << "\n";}}

using LL = long long;

//------------------------------------------
//------------------------------------------

int main() {

    int N;
    cin >> N;

    string S;
    cin >> S;

    int ans = 0;
    string T = "";

    for (auto c: S) {
        if (c == '1' or c == '9') T += c;
        else ans++;
    }

    int one = 0;
    int nine = 0;
    for (int i = 0; i < T.size(); i++) {
        if (T[i] == '1')one++;
        else {
            if (one) {
                one--;
                ans++;
            } else {
                nine++;
            }
        }
    }

    ans += min(nine / 2, one);
    one -= min(nine / 2, one);
    ans += one / 2;
    cout << ans << endl;

    return 0;
}