#include <bits/stdc++.h>
using namespace std;
int main() {
// your code goes here
int n;
cin>>n;
int *arr=new int[n];
for(int i=0;i<n;i++)
{
cin>>arr[i];
}
sort(arr,arr+n);
int d=1,c=0;
for(int i=0;i<n;i++)
{
if(d<=arr[i])
{
c++;
d++;
}
}
cout<<c;
delete arr;
return 0;
}
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