#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <chrono>
#define _USE_MATH_DEFINES
#include <cmath>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iostream>
#include <iomanip>
#include <iterator>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <utility>
#include <vector>
using namespace std;

#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

const int INF = 0x3f3f3f3f;
const long long LINF = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-8;
const int MOD = 1000000007; // 998244353;
const int dy[] = {1, 0, -1, 0}, dx[] = {0, -1, 0, 1};

struct IoSetup {
  IoSetup() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    cout << fixed << setprecision(20);
    cerr << fixed << setprecision(10);
  }
} iosetup;
/*-------------------------------------------------*/
int main() {
  int n; cin >> n;
  string s; cin >> s;
  string I9 = "";
  REP(i, n) {
    if (s[i] == '1' || s[i] == '9') {
      I9 += s[i];
    }
  }
  int ans = n - I9.length();
  int one = 0, nine = 0;
  for (char c : I9) {
    if (c == '1') {
      ++one;
    } else {
      if (one > 0) {
        --one;
        ++ans;
      } else {
        ++nine;
      }
    }
  }
  while (one > 0) {
    if (nine < 2) break;
    ++ans;
    --one;
    nine -= 2;
  }
  ans += one / 2;
  cout << ans << '\n';
  return 0;
}