include <bits/stdc++.h>

using namespace std; int a[1000005]; int main() {

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

}