#include<fstream>
using namespace std;

int main()
{
	int a,b,v[100000],n,nr=1;
	ifstream in("ciur.in");
	in>>n;
	in.close();
	for(a=2; a<=n; a++)
		v[a]=1;
	for(a=3; a*a<=n; a+=2)
		if(v[a]==1)
			for(b=3; b*a<=n; b++)
				v[a*b]=0;	
	for(a=3; a<=n; a+=2)
		if(v[a]==1)
			nr++;
	ofstream out("ciur.out");
	out<<nr;
	out.close();
	return 0;
  
}