#include<fstream>
#include<math.h>
using namespace std;

ifstream in ("ciur.in");

int main()
{
	int n, nr=0;
	bool prim;
	in>>n;
	in.close();

	if (n>=2) { nr=1;
		for (int i=3; i<=n;i+=2)
		{	prim=true;
			for (int x=2;x<=sqrt(i);x++)
				if (i%x==0) {prim=false; break; }
			if (prim) nr++;
		}
	}

	ofstream out ("ciur.out");
	out<<nr;
	out.close();

	return 0;
}