#include<stdio.h>
#include<stdlib.h>
using namespace std;
void merge(int arr[], int l, int m, int r)
{
    int i, j, k;
    int n1 = m - l + 1;
    int n2 =  r - m;
    int L[n1], R[n2];
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1+ j];
    i = 0;
    j = 0;
    k = l;
    while (i < n1 && j < n2)
    {
        if (L[i] <= R[j])
        {
            arr[k] = L[i];
            i++;
        }
        else
        {
            arr[k] = R[j];
            j++;
        }
        k++;
    }


    while (i < n1)
    {
        arr[k] = L[i];
        i++;
        k++;
    }


    while (j < n2)
    {
        arr[k] = R[j];
        j++;
        k++;
    }
}

void mergeSort(int arr[], int l, int r)
{
    if (l < r)
    {

        int m = l+(r-l)/2;
        mergeSort(arr, l, m);
        mergeSort(arr, m+1, r);

        merge(arr, l, m, r);
    }
}

int main()
{   int n,i,j,tmp,arr[200005],m=0,d;
    scanf("%d",&n);
        for(i=0;i<n;i++)
            {
                scanf("%d",&arr[i]);
            }
         mergeSort(arr, 0, n - 1);
            d=1;
            for(i=0;i<n;i++)
            {
                 if(arr[i]>=d)
                 {
                     d++;
                     m++;

                 }
            }

printf("%d",m);



    return 0;
}