#include <stdio.h>
#include <math.h>

long n,i,j,k,p,nr;
char a[2000001];

int main(){
  FILE *f = fopen("ciur.in", "r");
  FILE *g = fopen("ciur.out", "w");
  fscanf(f,"%ld", &n);

  for (i=2;i<=n;i++)
    if (!a[i])
      for (j=i+i;j<=n;j+=i)
	a[j]=1;

  for (i=2;i<=n;i++)
    if (a[i])
      nr++;

  fprintf(g,"%ld", nr);
  fclose(f);
  fclose(g);
  return 0;
}