#include <bits/stdc++.h>
using namespace std;

int daysOfHomework(int N, vector<int> &P)
{
    sort(P.begin(), P.end());

    int count = 1;
    for (int i = 0; i < N; i++)
    {
        if (P[i] >= count)
        {
            count++;
        }
    }

    return count - 1;
}

int main()
{
    int N;
    cin >> N;

    vector<int> P(N);
    for (int i = 0; i < N; i++)
    {
        cin >> P[i];
    }

    cout << daysOfHomework(N, P) << endl;
}