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