var v:array[1..2000000] of byte;
    n,i,j,k:integer;
    f,g:text;

begin
  assign(f,'ciur.in');
  reset(f);
  read(f,n);
  close(f);
  k:=0;
  for i:=2 to trunc(sqrt(n)) do
    begin
      if v[i]=0 then
        begin
          inc(k);
          j:=sqr(i);
          while j<=n do
            begin
              v[j]:=1;
              inc(j,i);
            end;
        end;
    end;
  assign(f,'ciur.out');
  rewrite(f);
  write(f,k);
  close(f);
end.