#include <stdio.h>
#define Nmax 2000000

long int n, nr;
char T[Nmax];
int main()
{
  FILE *fin=fopen ("ciur.in", "r");
  FILE *fout=fopen ("ciur.out", "w");
  long int i, j;
  fscanf (fin, "%ld\n", &n);
  for (i=2; i<n; i++)
    T[i]=1;
  for (i=2; i<n; i++)
    if (T[i]==1)
      {
	nr++;
	for (j=2; j*i<n; j++)
	  T[i*j]=0;
      }
  fprintf (fout, "%ld\n", nr);
  fclose(fout);
  return 0;
}