просвещайтесь http://ru.wikipedia.org/wiki/%D0%A1%D0%B0%D0%B9%D0%B3%D0%B0_(%D0%BE%D0%B3%D0%BD%D0%B5%D1%81%D1%82%D1%80%D0%B5%D0%BB%D1%8C%D0%BD%D0%BE%D0%B5_%D0%BE%D1%80%D1%83%D0%B6%D0%B8%D0%B5)