var currentSlide = 1;

function slide(newSlide) {
    if (currentSlide != newSlide) {
        $("#slide" + currentSlide).hide();
        $("#slide" + newSlide).show();
        currentSlide = newSlide;
    }
}

function slideNext() {
    if ($("#slide" + (currentSlide + 1)).length > 0)
        slide(currentSlide + 1);
    else
        slide(1);
}