#include<stdio.h>
#define N 2000001
bool ciur[N];
int n;
void ciur_eratostene (){
  int d,i;
  for (d=2;d*d<n;d++)
    if (ciur[d] == 0)
      for (i=d*d;i<=n;i+=d)
        ciur[i] = 1;
}

int main (){
  FILE *in,*out;
  in = fopen ("ciur.in","r");
  out = fopen ("ciur.out","w");
  int i,cate;
  fscanf(in,"%d",&n);

  ciur_eratostene ();

  cate = 0;
  for (i=2;i<=n;i++)
    if (ciur[i] == 0)
      cate ++;
  fprintf (out,"%d",cate);

  fclose (in);
  fclose (out);
  return 0;
}