if (!document.getElementById)
    document.getElementById = function() { return null; }


function changeSlide(direction, slideCount) {

  slideToHide = document.getElementById("slide" + currentSlide);
  
  if (direction == "next") {
    currentSlide += 1;
  } else {
    currentSlide -= 1;
  }
  if (currentSlide == 0) currentSlide = slideCount;
  if (currentSlide > slideCount) currentSlide = 1;
  
  slideToShow = document.getElementById("slide" + currentSlide);
  
  slideToShow.style.display = "block";
  slideToHide.style.display = "none";
}