#include<fstream>
#include<cmath>

using namespace std;

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


char p[2000005];
int n,nr;

void count();
int prim(int x);

int main()
{
	f>>n;
	count();
	g<<nr<<'\n';
	f.close();
	g.close();
	return 0;
}


void count()
{
	int i=-1,k;
	nr=n-1;
	for(i=1;i<=n;p[i]=1,++i);
	for (i=2;i<=n;++i)
	{
		if (p[i])
		for (k=i+i;k<=n;k+=i)
			if (k<=n&&p[k])
			{
				p[k]=0;
				--nr;
			}
	}
}