#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;  
}