#include <iostream>
#include <fstream>
 using namespace std;
  int main()
  {    int n,i,j,nr=1; 
     char a[2000002]; 
  ifstream f("ciur.in"); 
      f>>n;    f.close();   
       for (i=3;i<=n;i+=2) 
           a[i]=1;   
        for (i=3;i<=n;i+=2) 
             {     
                  if (a[i]==1)  
                    {        
                       nr++; 
                   for (j=3*i;j<=n;j+=2*i)   
                          a[j]=0;  
                                } 
                                    } 
              ofstream g("ciur.out");  
      g<<nr;   g.close();  
system("pause");
   return 0;}