#include <atcoder/maxflow.hpp>
#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;
using vl = vector<ll>;
#define rep3(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define rep2(i, a, b) rep3(i, a, b, 1)
#define rep1(i, n) rep2(i, 0, n)
#define rep0(n) rep1(aaaaa, n)
#define ov4(a, b, c, d, name, ...) name
#define rep(...) ov4(__VA_ARGS__, rep3, rep2, rep1, rep0)(__VA_ARGS__)
#define per(i, a, b) for (ll i = (a) - 1; i >= (b); i--)
#define fore(e, v) for (auto &&e : v)
#define all(a) begin(a), end(a)
#define sz(a) (int)(size(a))
#define lb(v, x) (lower_bound(all(v), x) - begin(v))
#define eb emplace_back

template <typename T, typename S> bool chmin(T &a, const S &b) {
  return a > b ? a = b, 1 : 0;
}
template <typename T, typename S> bool chmax(T &a, const S &b) {
  return a < b ? a = b, 1 : 0;
}
const int INF = 1e9 + 100;
const ll INFL = 3e18 + 100;
#define i128 __int128_t
struct _ {
  _() { cin.tie(0)->sync_with_stdio(0), cout.tie(0); }
} __;

int main() {
  int N;
  cin >> N;
  int MAX_A = 5000;
  vi cnt(MAX_A + 1);
  rep(N) {
    int A;
    cin >> A;
    cnt[A]++;
  }
  int NG = MAX_A + 1, OK = 1;
  while (NG - OK > 1) {
    int mid = (OK + NG) / 2;
    atcoder::mf_graph<int> G(mid + MAX_A + 2);
    int source = mid + MAX_A, sink = mid + MAX_A + 1;
    rep(i, 1, MAX_A + 1) { G.add_edge(source, i - 1, cnt[i]); }
    rep(i, 1, mid + 1) {
      rep(j, i, MAX_A + 1, i) { G.add_edge(j - 1, MAX_A + i - 1, 1); }
      G.add_edge(MAX_A + i - 1, sink, 1);
    }
    int s = G.flow(source, sink);
    if (s == mid)
      OK = mid;
    else
      NG = mid;
  }
  cout << OK << '\n';
}