#include <fstream>
 using namespace std; 
    	ifstream in("ciur.in");
	ofstream out("ciur.out");  
    int N, cnt;  
    char prim[2000005];  
      
    int main(void)  
    {  
        int i, j;  
          
    
    
  	in>>N;   
    
       for (i = 2; i <= N; ++i)  
           prim[i] = 1;  
       for (i = 2; i <= N; ++i)  
           if (prim[i])  
           {  
               ++cnt;  
               for (j = i+i; j <= N; j += i)  
                   prim[j] = 0;  
           }  
     
  
  out<<cnt;   
       return 0;  
   }