program ciurul;
   var n,i,j,k:longint;
       a : array [1..2000000] of boolean;
       fi,fo:text;
begin
  assign(fi,'ciur.in');
   reset(fi);
  assign(fo,'ciur.out');
   rewrite(fo);
  read(fi,n);
  for i:=2 to n do begin
                if not a[i] then begin
                                  inc(k);
                                   for j:=2 to n div i do
                                     a[i*j]:=true;
                                      end;
                   end;

     write(fo,k);
  close(fo);
end.