window.addEvent('domready', function () {
    /* settings */
    var showDuration = 20000;
    var container = $('slideshow-container');
    var images = container.getElements('span');
    var currentIndex = 0;
    var interval;
    /* opacity and fade */
    images.each(function (img, i) {
        if (i > 0) {
            img.set('opacity', 0);
        }
    });
    /* worker */
    var show = function () {
        images[currentIndex].fade('out');
        images[currentIndex = currentIndex < images.length - 1 ? currentIndex + 1 : 0].fade('in');
    };
    /* start once the page is finished loading */
    window.addEvent('load', function () {
        interval = show.periodical(showDuration);
    });
});