Program Ciurul;
               uses crt;
               var i, j : longint;
                   a : array[1..2000000] of longint;
                   n, nr : longint;
                   fi, fo : text;
begin clrscr;
             assign(fi,'ciur.in'); reset(fi);
             assign(fo,'ciur.out'); rewrite(fo);
             read(fi,n);
             nr:=0;
             for i:=2 to n do begin
                                   if a[i]=0 then begin
                                                      NR:=NR+1;
              for j:=2 to n do begin
                                   if i*j>n then break else a[i*j]:=1;
                               end;
                      end;
              end;
              write(fo,nr);
      close(fo);
end.