#include <stdio.h>

FILE *f,*g;
char a[2000005];
long n,contor,i,j;

int main()
{
  f=fopen("ciur.in","r");
  g=fopen("ciur.out","w");
  fscanf(f,"%ld\n",&n);
  for(i=2;i<=n/2;i++)
    if(a[i]!=1)
      for(j=2*i;j<=n;j+=i)
	  a[j]=1;
  for(i=2;i<=n;i++)
    if(a[i]==0)
	  contor++;
  fprintf(g,"%ld\n",contor);
  fclose(f);  fclose(g);
  return 0;
}