// May this submission get accepted!

#pragma GCC optimize ("O3")
#pragma GCC target ("tune=native")
#pragma GCC target ("avx")

#include <bits/stdc++.h>

// 汎用マクロ
#define ALL_OF(x) (x).begin(), (x).end()
#define REP(i,n) for (long long i=0, i##_len=(n); i<i##_len; i++)
#define RANGE(i,is,ie) for (long long i=(is), i##_end=(ie); i<=i##_end; i++)
#define DSRNG(i,is,ie) for (long long i=(is), i##_end=(ie); i>=i##_end; i--)
#define STEP(i, is, ie, step) for (long long i=(is), i##_end=(ie), i##_step = (step); i<=i##_end; i+=i##_step)
#define UNIQUE(v) do { sort((v).begin(), (v).end()); (v).erase(unique((v).begin(), (v).end()), (v).end()); } while (false)
template<class T> bool chmax(T &a, const T &b) {if (a < b) {a = b; return true;} return false; }
template<class T> bool chmin(T &a, const T &b) {if (a > b) {a = b; return true;} return false; }
#define INF 0x7FFFFFFF
#define LINF 0x7FFFFFFFFFFFFFFFLL
#define Yes(q) ((q) ? "Yes" : "No")
#define YES(q) ((q) ? "YES" : "NO")
#define Possible(q) ((q) ? "Possible" : "Impossible")
#define POSSIBLE(q) ((q) ? "POSSIBLE" : "IMPOSSIBLE")
#define DUMP(q) cerr << "[DEBUG] " #q ": " << (q) << " at " __FILE__ ":" << __LINE__ << endl
#define DUMPALL(q) do { cerr << "[DEBUG] " #q ": ["; REP(i, (q).size()) { cerr << (q)[i] << (i == i_len-1 ? "" : ", "); } cerr << "] at " __FILE__ ":" << __LINE__ << endl; } while (false)
template<class T> T gcd(T a, T b) { if (a < b) std::swap(a, b); while (b) std::swap(a %= b, b); return a; }
template<class T> T lcm(const T a, const T b) { return a / gcd(a, b) * b; }

// gcc拡張マクロ
#define popcount __builtin_popcount
#define popcountll __builtin_popcountll

// エイリアス
#define DANCE_ long
#define ROBOT_ unsigned
#define HUMAN_ signed
#define CHOKUDAI_ const
using  ll = DANCE_ HUMAN_ DANCE_;
using ull = DANCE_ ROBOT_ DANCE_;
using cll = DANCE_ DANCE_ CHOKUDAI_;
using  ld = long double;
using namespace std;

// モジュール


// 処理内容
int main() {
    
    // インタラクティブ問題では除去した方がいいかも
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    ll n; cin >> n;
    string s; cin >> s;

    // 3, 5, 7
    ll sz = s.size();
    s.erase(remove_if(ALL_OF(s), [](char c){
        return c == '3' || c == '5' || c == '7';
    }), s.end());

    ll ans = sz - (ll)s.size();

    vector<bool> used(s.size(), 0);

    // 19
    {
        ll l = 0, r = s.size() - 1;
        deque<ll> ones, nines;
        REP(i, s.size()) {
            if (s[i] == '1') {
                ones.push_back(i);
            } else if (s[i] == '9') {
                nines.push_back(i);
            }
        }
        while (ones.size() && nines.size()) {
            while (ones.size() && nines.size() && ones.front() > nines.front()) {
                nines.pop_front();
            }
            if (ones.size() && nines.size()) {
                used[ones.front()] = used[nines.front()] = true;
                ones.pop_front();
                nines.pop_front();
                ans++;
            }
        }
    }

    // 991
    ll nines = 0, ones = 0;
    REP(i, s.size()) if (!used[i]) {
        (s[i] == '1' ? ones : nines)++;
    }

    ll n991 = min(nines / 2, ones);
    ans += n991;
    nines -= n991 * 2;
    ones -= n991;

    // 11
    ans += ones / 2;

    cout << ans << endl;
    
}