#include <stdio.h>  
      
    int N, cnt;  
    char prim[2000005];  
      
    int main(void)  
    {  
        int i, j;  
          
      freopen("ciur.in", "r", stdin);  
       freopen("ciur.out", "w", stdout);  
     
       scanf("%d", &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;  
          }  
     
       printf("%d\n", cnt);  
     
       return 0;  
   }