27. It only takes 10 lines of vanilla JS
to do what we wanted
var current = 0,
slides = document.getElementsByTagName("img");
!
setInterval(function() {
for (var i = 0; i < slides.length; i++) {
slides[i].style.opacity = 0;
}
current = (current != slides.length - 1) ? current + 1 : current = 0;
slides[current].style.opacity = 1;
}, 3000);
300 bytes vs 49.000