#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>();
    int res = 0;
    int num1 = 0, num3 = 0, num5 = 0, num7 = 0, num9 = 0;
    rep(i, N) {
        if(s[i] == '1') {
            num1++;
        } else if(s[i] == '3') {
            num3++;
        } else if(s[i] == '5') {
            num5++;
        } else if(s[i] == '7')
            num7++;
        else
            num9++;
    }
    res += min(num9, num7);
    num7 -= min(num9, num7);
    res += num1 / 2;
    num1 -= 2 * num1 / 2;
    res += min(num1, num3);
    num3 -= min(num1, num3);
    res += num3 + num5 + num7;
    cout << res << endl;
}