#include <fstream>
using namespace std;

ifstream in("ciur.in");
ofstream out("ciur.out");

const int N=2000001;
bool c[N];

int main ()
{
	int n,j,nr=0;
	in>>n;
	for (int j=4;j<=n;j+=2)
		c[j]=true;
	for (int i=3;i*i<=n;i+=2)
		if (!c[i])
			for (j=i*i;j<=n;j+=i)
				c[j]=true;
	for (int i=2;i<=n;i++)
		if (c[i]==false)
			nr++;
	out<<nr;
	in.close();
	out.close();
}