function updateSlideNumber()
{
	var slideNumber = "" + visibleSlideNumber + " / " + numberOfSlides;
	document.getElementById("SlideNumber").innerHTML = slideNumber;
}

function nextSlide()
{
	var previousslideId = "Slide" + visibleSlideNumber;
	var previousslideDiv = document.getElementById(previousslideId);
	previousslideDiv.style.visibility="hidden";
 
	visibleSlideNumber = visibleSlideNumber + 1;
	if(visibleSlideNumber > numberOfSlides)
		visibleSlideNumber = 1;
	
	var nextSlideId = "Slide" + visibleSlideNumber;
	var nextSlideDiv = document.getElementById(nextSlideId);
	nextSlideDiv.style.visibility="visible";	
	
	updateSlideNumber();
}

function previousSlide()
{
	var currentSlideId = "Slide" + visibleSlideNumber;
	var currentSlideDiv = document.getElementById(currentSlideId);
	currentSlideDiv.style.visibility="hidden";
	
	visibleSlideNumber = visibleSlideNumber - 1;
	if(visibleSlideNumber == 0)
		visibleSlideNumber = numberOfSlides;
	
	var newSlideId = "Slide" + visibleSlideNumber;
	var newSlideDiv = document.getElementById(newSlideId);
	newSlideDiv.style.visibility="visible";
	
	updateSlideNumber();
}