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