#ifdef LOCAL
#define _GLIBCXX_DEBUG
#endif
#include <bits/stdc++.h>
#define ull unsigned long long
#define pll pair<ll, ll>
#define mp make_pair
#define ll long long
#define pb push_back
#define deb(x) cout << #x << " = " << x << endl
#define all(x) x.begin(), x.end()
#define ld long double
const ll mod1 = (ll)1e9 + 7;
const ll mod2 = (ll)1e9 + 9;
const ll BASE = 47;
const ll inf = (ll)1e18;
const long double e = 2.718281828459;
const long double pi = 3.141592653;
const ld EPS = 1e-9;
using namespace std;
template <class T>
istream& operator>>(istream &in, vector<T> &arr) {
for (T &cnt : arr) {
in >> cnt;
}
return in;
};
void solve() {
ll n;
cin >> n;
vector<ll> c(n);
cin >> c;
sort(all(c));
reverse(all(c));
for (int i = 0; i < n; i++) {
if (c[i] < i + 1) {
cout << i;
return;
}
}
cout << n;
}
int main() {
#ifndef LOCAL
ios_base::sync_with_stdio(0);
cin.tie(0);
cout.tie(0);
#else
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
cout.precision(30);
ll seed = time(0);
//cerr << "Seed: " << seed << "\n";
srand(seed);
solve();
return 0;
}
