include

using namespace std;

const int N = 1000010; int a[N], t[N];

int main() {

int n;
cin >> n;
int x;
for (int i = 0; i < n; i++) {
	cin >> x;
	t[x]++;
}
int i = 0, j = 0;
while (j <= n) {
	while (t[j] && i <= j) {
		i++;
		t[j]--;
	}
	j++;
}
cout << i;

return 0;

}