#include <fstream>

using namespace std;

ifstream fin("div3.in");
ofstream fout("div3.out");

int prim(long long unsigned );

long long unsigned n, k;

int main()
{
	fin>>n;
	long long unsigned i=0;
	for(i=2; i*i<=n; i++)
	{
		if(prim(i))
			k++;
	}
	fout<<k;
	return 0;
}
int prim(long long unsigned x)
{
	long long unsigned i=0;
	if(x==1)
		return 0;
	if(x%2==0 && x!=2)
		return 0;
	for(i=3; i<=x/2; i+=2)
		if(x%i==0)
			return 0;
	return 1;
}