function change_slide()
{

	var slideId = 'slide'+ slide;
	var previousSlideId = 'slide' + previousSlide;
	var slideElement = document.getElementById(slideId);
	slideElement.style.display = 'block';
	var previousSlideElement = document.getElementById(previousSlideId);
	previousSlideElement.style.display = 'none';

}

var slide = 1;

function next_slide(end)
{

	previousSlide = slide;
	
	if (slide != end){
		slide += 1;
	}else{
		slide = 1;
	}
	
	if(end > 1){
		change_slide();
	}
}

function previous_slide()
{
	
	previousSlide = slide;

	if (slide != 1){
		slide -= 1;
	}else{
		slide = 1;
		previousSlide = 0;
	}
	
	change_slide();

}