#include<stdio.h>

int main(void)
{
 freopen("ciur.in","r",stdin);
 freopen("ciur.out","w",stdout);
 char prim[2000000];
 long n,k=1,i,j;
 scanf("%ld",&n);
 for(i=2; i<=n; i++) prim[i]=1;
 for(i=3; i<=n; i+=2)
 if(prim[i])
 {
  k++;
  for (j=i+i; j<=n; j+=i) prim[j]=0;
 }
 printf("%ld\n",k);
 return 0;
}