include <bits/stdc++.h>

using namespace std;

int a[10000005] = {0};

int main() {

//freopen("mooncake.in", "r", stdin);
//freopen("mooncake.out", "w", stdout);
int n;
cin >> n;
int c = 0;
for (int i = 0; i < n; i++) {
	int b;
	cin >> b;
	a[b]++;
}
for (int i = 1; i <= n; i++) {
	c += a[i-1];
	if (c > i) {
		c = i;
	}
}
cout << c;

}