#include <bits/stdc++.h>
#define REP(i, n) for(int i = 0;i < n;i++)
#define VSORT(v) sort(v.begin(), v.end())
#define VRSORT(v) sort(v.rbegin(), v.rend())
#define ll long long
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
typedef pair<int, P> PP;
typedef pair<ll, LP> LPP;
//typedef vector<unsigned int>vec;
typedef vector<ll>vec;
typedef vector<vec> mat;
typedef vector<vector<int>> Graph;

const int dx[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dy[8] = {0, 1, 0, -1, 1, 1, -1, -1};
const int INF = 1000000000;
const ll LINF = 1000000000000000000;//1e18
const ll  MOD = 1000000007;
//const ll MOD = 998244353;
const double PI = acos(-1.0);
const double EPS = 1e-10;

template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline void add(T &a, T b){a = ((a+b) % MOD + MOD) % MOD;};

int main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    string S;
    cin >> S;
    map<int, int> mp;
    REP(i,n){
        int m = S[i] - '0';
        mp[m]++;
    }
    ll ans = mp[1] / 2;
    if(mp[1] % 2 == 1){
        if(mp[9] > 0) ans++, mp[9]--;
        else if(mp[3] > 0){
            ans++, mp[3]--;
        }
        else if(mp[5] > 0) ans++, mp[5]--;
        else if(mp[7] > 0) ans++, mp[7]--;
    }
    if(mp[9] > 0 && mp[3] > 0){
        if(mp[9] > mp[3]) ans += mp[3], mp[9] -= mp[3], mp[3] = 0;
        else ans += mp[9], mp[3] -= mp[9], mp[9] = 0;
    }
    if(mp[9] > 0 && mp[5] > 0){
        if(mp[9] > mp[5]) ans += mp[5], mp[9] -= mp[5], mp[5] = 0;
        else ans += mp[9], mp[5] -= mp[9], mp[5] = 0;
    }
    if(mp[9] > 0 && mp[7] > 0){
        if(mp[9] > mp[7]) ans += mp[7], mp[9] -= mp[7], mp[7] = 0;
        else ans += mp[9], mp[7] -= mp[9], mp[7] = 0;
    }
    ans += mp[3] + mp[5] + mp[7];
    cout << ans << endl;
}