var visibleSlide = 1;

var slidesCount = 4;

function showNextSlide() 
{
	var slideToShow = visibleSlide + 1;
	if (slideToShow > slidesCount)
		slideToShow = 1;
	showSlide(slideToShow);
}

function showPrevSlide() 
{
	var slideToShow = visibleSlide - 1;
	if (slideToShow < 1)
		slideToShow = slidesCount;
	showSlide(slideToShow);
}

function showSlide(slideNum)
{
	for (var i=1; i <= slidesCount; i++) {
		document.getElementById("slide-slide-" + i).style.display = ((i == slideNum) ? "block" : "none");
	}
	visibleSlide = slideNum;
}