#include<iostream.h>
#include<fstream>
using namespace std;
ifstream f ("ciur.in");
ofstream g ("ciur.out");
long long ciur[200005],n,i,j,nr;
int main ()
{
	
	f>>n;
	for ( i=2; i<n; i++ )
		ciur[i]=1;
	for ( i=2; i*i<=n; i++)
		if (ciur[i])
			for ( j=2; j*i<n; j++ )
				ciur[i*j]=0;
	for ( i=2; i<n; i++ )
		if ( ciur[i])
			nr++;
	g<<nr;	
}