#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  int a[n];
  for (long long i = 0; i < n; i++) cin >> a[i];
  sort(a, a + n);
  int c = 1, d = 0;
  for (int i = 0; i < n; i++) {
    if (a[i] >= c) {
      c++;
      d++;
    }
  }
  cout << d << endl;
}
