#include<stdio.h>
#include<string.h>
FILE*fin=fopen("ciur.in","r");
FILE*fout=fopen("ciur.out","w");
int n,nrp=0;
char p[2000001];
int main()
{
  int i,j;
  fscanf(fin,"%d",&n);
  fclose(fin);
  memset(p,0,sizeof(p));
  for(i=2;i<=n;i++)
    if(!p[i])
    {
      nrp++;
      for(j=i*i;j<=n&&j>i;j+=i)
	p[j]=1;
    }
  fprintf(fout,"%d",nrp);
  fclose(fout);
  return 0;
}