//Ciurul lui Eratostene
#include<fstream.h>
ifstream f("ciur.in");
ofstream g("ciur.out");
long x,n,y,v[2000001],s;
int main()
{
	f>>n;
	s=0;
	for(x=2;x<=n;x++)
	{	if(v[x]==0)
		y=2;
		while (y*x<=n)
			{v[y*x]=1;
		    y++;}
	}
	for(x=1;x<=n;x++)
       if (!v[x])
            s++;
    g<<s-1<<'\n';
	f.close();
	g.close();
	return 0;
}