uses crt;
const
  abc = ['a'..'z'];
  s: string = '      yes yes no yes no for for for for.';

var
  s_res, prev, _word: string;
  p: byte;

begin
  clrscr;
  s_res := s; prev := '';

  p := 1;
  repeat
    while not (s_res[p] in abc) and (p <= length(s_res))
      do inc(p);

    while (s_res[p] in abc) and (p <= length(s_res)) do begin
      _word := _word + s_res[p];
      inc(p);
    end;

    if _word = prev then begin
      delete(s_res, p - length(_word), length(_word));
      dec(p, length(_word));
    end
    else prev := _word;

    _word := '';

  until p > length(s_res);
  writeln(s_res);
  readln;
end.