#include<fstream>
using namespace std;
int prim(int i)
{
	unsigned int ok=1,k;
	for(k=2;k<=i/2;k++)
		if(i%k==0)
			goto aa;
		//if(i/k<k)
			//goto aa;
	return 1;
	aa:;
	return 0;
}
int main()
{
	unsigned int i,nr,k=0;
	ifstream fin("ciur.in");
	ofstream fout("ciur.out");
	fin>>nr;
	for(i=2;i<=nr;i++)
		if(prim(i)==1)
			k++;
	fout<<k;
}