#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 i = s.size() - 1;
  int ans = 0;
  while (i >= 0) {
    if (s[i] == '3' || s[i] == '5' || s[i] == '7') {
      ans++;
      i--;
    } else if (s[i] == '1') {
      if (i >= 1 && s[i - 1] == '1') {
        ans++;
        i -= 2;
      } else if (i >= 2 && s[i - 1] == '9' && s[i - 2] == '9') {
        ans++;
        i -= 3;
      } else {
        i--;
      }
    } else if (s[i] == '9') {
      if (i >= 1 && s[i - 1] == '1') {
        ans++;
        i -= 2;
      } else if (i >= 1 && s[i - 1] == '5') {
        ans++;
        i -= 2;
      } else {
        i--;
      }
    }
  }
  cout << ans << endl;
}