#include <stdio.h>
//#include <mem.h>
int v[20001];
int main(){
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    long n,i,j;
    scanf("%ld",&n);
    //printf("%d",n);
  // memset(v,0,sizeof(v));
   for(i=4;i<=n;i+=2)v[i]=1;
    for(i=3;i<=n;i+=2){
                       if(!v[i])for(j=i*i;j<=n;j+=i+i)v[j]=1;
                       }
    long num;
    num=0;
    for(i=2;i<=n;i++)if(!v[i]) num++;  //   printf(" %d ",i);}
     printf("%ld",num);
    
    
    return 0;
}