# include <fstream>  
 #define N 2000001    
 using namespace std;  
   int i;
 char c[N];    
 long  n;    
 void ciur()    
{  
  int d=2;    
    while (d*d<=n)    
     { if (!c[d])    
         for (i=d*d; i<=n; i+=d)    
            c[i]=1;++d;    
       }    
 long  num=0;    
  for ( i=2; i<=n; ++i)   
     if (!c[i])
       num++;    
      
 ofstream g("ciur.out");  
  g<<num;  
  g.close();  
 }
     
  void citire()
{ ifstream f("ciur.in");    
   f>>n;    
 f.close();  
  }    
 
 int main()    
 {  citire();    
    ciur();    
    return 0;    
}