#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');
    int one = 0;
    int u = 0;
    for(int i = 0;i < N;i++){
        if(S[i] == '1'){
            one++;
        }
        if(S[i] == '9' && one != 0){
            u++;
            one--;
        }
    }
    ans += u;
    ans += (count(S.begin(), S.end(), '1') - u)/2;
    cout<<ans<<endl;
}