include <bits/stdc++.h>

using namespace std; int a[1000005];

int main() {

int n;
cin >> n;
for (int i = 0; i < n; i++) {
	int x;
	cin >> x;
	a[x]++;
}
int ans = 0;
for (int i = 1; i <= n; i++) {
	ans += a[i - 1];
	if (ans > i)
		ans = i;
}
cout << ans;

return 0;

}