#include<stdio.h>
FILE *f=fopen("ciur.in","r"),
     *g=fopen("ciur.out","w");
char a[2000010];
int i,n,nr,k;
int main()
{ fscanf(f,"%d",&n);
  nr=1;
  for(i=3;i<=n;i+=2) {
                      if(!a[i]) nr++;
                      for(k=i*i;k<=n;k+=i+i) a[k]=1;
                    }
  fprintf(g,"%d\n",nr);
  fclose(f);
  fclose(g);
  return 0;
}