#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
  }
  sort(a, a + n);
  int d = 1;
  for (int i = 0; i < n; ++i) {
    if (a[i] >= d) {
      d++;
    }
  }
  cout << d - 1;
  return 0;
}
