#include <stdio.h>
#include <bitset>

using namespace std;

long N,i,j,q,p[1002];
bitset <2097152>prim;

int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    
    scanf("%ld",&N);
    
    prim.set();
    prim[1]=0;
    for (i=2;i<=N;i++)
        if (prim[i]){
           q++;
           for (j=i+i;j<=N;j+=i)
               prim[j]=0;
        }
    printf("%ld\n",q);
    /*
    if (q<=1000){
       for (i=2;i<=N;i++)
           if (prim[i])printf("%ld ",i);
       printf("\n");
    }
    else{
         q=1000;
         i=N;
         while (q){
               if (prim[i]){p[q]=i;q--;}
               i--;
         }
         for (i=1;i<=1000;i++)
             printf("%ld ",p[i]);
         printf("\n");
    }
     */  
return 0;
}