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

int a[1000005];

int main()
{
	int n, cnt = 0;
	cin >> n;
	for (int i = 1; i <= n; i++) cin >> a[i];
	sort(a + 1, a + n + 1);
	for (int i = 1; i <= n; i++)
		if (a[i] >= i) cnt++;
		else {cout << cnt; return 0;}
	cout << cnt;
	return 0;
 } 

dalao求助、、、