# include <fstream>  
 #define N 2000001    
 using namespace std;  
   
 char c[N];    
 long long n;    
 void ciur()    
{    
     int d=2;    
     while (d*d<=n)    
     {    
        
      if (!c[d])    
          for (int i=d*d; i<=n; i+=d)    
               c[i]=1;++d;    
    }    
    long long num=0;    
     for (int 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;    
}