#include <bits/stdc++.h>
using namespace std;
const long long int mod = 1000000000 + 7;
const long long int N = 10000000 + 6;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  int n;
  cin >> n;
  int arr[n];
  for (int i = 0; i < n; i++) cin >> arr[i];
  sort(arr, arr + n);
  int curr = 1;
  for (int i = 0; i < n; i++) {
    if (arr[i] >= curr) curr++;
  }
  cout << curr - 1;
}
