#include <bits/stdc++.h>

using namespace std;
using ll = long long;

const int MOD = 1e9+7;

int main()
{
    int N;
    string S;
    cin >> N;
    cin >> S;
    int ans = 0;
    ans += count(S.begin(), S.end(), '7');
    ans += count(S.begin(), S.end(), '3');
    ans += count(S.begin(), S.end(), '5');
    ans += count(S.begin(), S.end(), '1') / 2;
    cout<<ans<<endl;
}