#include <bits/stdc++.h>

#define rep(i, n) for (int i = 0; i < (n); i++)
#define repr(i, n) for (int i = (n) - 1; i >= 0; i--)
#define rep2(i, l, r) for (int i = (l); i < (r); i++)
#define rep2r(i, l, r) for (int i = (r) - 1; i >= (l); i--)
#define range(a) a.begin(), a.end()

using namespace std;
using ll = long long;

int main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(15);
  int n; cin >> n;
  string s; cin >> s;
  int ans = 0;
  int cnt[10] = {};
  rep(i, n) {
    if (s[i] == '9' && cnt[1] > 0) {
      ans++;
      cnt[1]--;
    } else {
      cnt[s[i] - '0']++;
    }
  }
  ans += cnt[1] / 2;
  ans += cnt[3];
  ans += cnt[5];
  ans += cnt[7];
  cout << ans << endl;
}