#include <fstream>
#define NMAX 2000002
using namespace std;

fstream intrare ("ciur.in",ios::in);
fstream iesire ("ciur.out",ios::out);
int sir[NMAX],N,contor;
void construire()
{
 for (int i=2;i<=N;i++)
   {
      if(sir[i]==0)
      {
          contor++;      
          for(int j=i+i;j<=N;j+=i)
          sir[j]=1;       
      }       
   } 
}
int main()
{
 intrare>N;
 
 construire();
 iesire<<contor;
}