#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;  
}