Slider

$( document ).ready(function() {
    var index = 1;
    $('.slide').hide();
    $('#slideshow div:nth-child(1)').show();

    window.setInterval(changeSlide, 2000);

    $('button#next').on('click', function() {
        changeSlide();
    })

    $('button#back').on('click', function() {
        $('#slideshow div:nth-child(' + index + ')').fadeOut();
        index--;
        if (index < 1) {
            index = 3;
        };
        $('#slideshow div:nth-child(' + index + ')').fadeIn();
    })

    function changeSlide() {
        $('#slideshow div:nth-child(' + index + ")").fadeOut('slow');
        index++;
        if (index > 3) {
            index = 1;
        };
        $('#slideshow div:nth-child(' + index + ")").fadeIn('slow');
    }

});