uses crt;

procedure show_file(var f: text; var before: integer);
var
  i: integer;
  s: string;
begin
  reset(f);

  for i := 1 to before do readln(f, s);
  gotoxy(1, 1);

  if seekeof(f) and (before > 0) then dec(before)
  else
    while (wherey < 24) and (not seekeof(f)) do begin
      readln(f, s);
      write(s); clreol; writeln;
    end;


  for i := wherey to 24 do begin
    gotoxy(1, i); clreol;
  end;
end;

var
  ch: char;
  scrolled_up: integer;
  f: text;

begin
  assign(f, 'sc_me.txt');
  reset(f);

  scrolled_up := 0;

  while true do begin

    show_file(f, scrolled_up);
    ch := readkey;
    case ch of
      #0:
        case readkey of
          #72: if scrolled_up > 0 then dec(scrolled_up);
          #80: inc(scrolled_up);
        end;
      #27: break;
    end;

  end;

  close(f);
end.