#include<stdio.h>
FILE *f,*g;
long i,n,j,nr; char viz[2500000];
int main()
{ f=fopen("ciur.in","r"); g=fopen("ciur.out","w");
  fscanf(f,"%ld",&n);
  i=2;
  while(i<=n)
   { if(viz[i]!='1') 
      { nr++; j=2*i; while(j<=n) { viz[j]='1'; j+=i; }}
     if(i!=2) i+=2; else i++;
   }
  fprintf(g,"%ld",nr);
  fclose(g);
  return 0;
}