#include <fstream>
using namespace std;
int main ()
{
	int n,i,j,v[10001],nr=0;
	ifstream fcin ("ciur.in");
	ofstream fcout ("ciur.out");
	fcin>>n;
	for (i=2;i<=n;i++)
		v[i]=1;
	for (i=2;i<=n;i++)
		if (v[i]==1)
			for (j=2*i;j<=n;j+=i)
				v[j]=0;
	for (i=2;i<=n;i++)
		if (v[i]==1)
			nr++;
	fcout<<nr;
	fcin.close ();
	fcout.close ();
	return 0;
}