#include<fstream>
using namespace std;
int v[2000001];
int main ()
{
	int c=0,i,n,j;
	ifstream is("ciur.in");
	ofstream os("ciur.out");
	is>>n;
	for (i=2;i<=n;i++)
	{
	   if (v[i]==0)
	   {
		   c++;
	   }
	   for (j=i;j<=n;j++)
	   {
		   v[i*j]=1;
	   }
	}
	os<<c;
	return 0;
}