#include <fstream.h>  
   int N, cnt;  
   char prim[2000005];  
   int main()  
   {  
      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;  
   }