#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;  
 }