#include<fstream>
#include<math.h>
using namespace std;
int prim(int x)
{
	int i;double t=x;
	if(x%2==0) return 0;
	for(i=3;i<=sqrt(t);i+=2)
		if(x%i==0) return 0;
	return 1;
}
int main ()
{
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	int n,s=1,i;
	fin>>n;
	for(i=3;i<=n;i+=2)
		if(prim(i)==1) s++;
	fout<<s;
	fin.close ();
	fout.close ();
	return 0;
}