#include<stdio.h>
FILE *f=fopen("ciur.in","r"),
     *g=fopen("ciur.out","w");
char a[2000003];
int i,n,nr,k;
int main()
{ fscanf(f,"%d",&n);
  for(i=2;i<=n;i++) { if(!a[i]) nr++;
                     for(k=i;i*k<=n;k++) a[i*k]=1;
                    }
  fprintf(g,"%d\n",nr);
  fclose(f);
  fclose(g);
  return 0;
}