include <bits/stdc++.h>

using namespace std; int d[10000005];

int main() {

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

}