#include<iostream>
#include<fstream>
using namespace std;
unsigned short a[2000005];
int main()
{ unsigned short n,i,j,c=1;
  ifstream fin("ciur.in");
  ofstream fout("ciur.out");
  fin>>n;
  for(i=4;i<=n;i=i+2)
  {
	  a[i]=1;
  }
  for(i=3;i<=n;i=i+2)
  {
	  if(a[i]==0)
	  {
		  for(j=2*i;j<=n;j=j+i)
	     {
		  a[j]=1;
	     }
	  }
	  if(a[i]==0) c++;
  }
  fout<<c;
  fin.close();
  fout.close();
  return 0;
}