var count = 0;
var thumbNumRight
var thumbNumLeft

function next(upper, URL, start) {
  var picture = "images/photos/" + URL;
	var thumb = "images/photos/thumbnails/" + URL;
	
  count++;
	
	var previous = count-1
	
  if (count == upper) {
  count = start;
	previous = upper;
  }
	
  document.slideshow.src = "images/photos/" + URL + count + ".jpg";
	document.previous.src = thumb + previous + ".jpg";
	document.next.src = thumb + (count+1) + ".jpg";
}

function previous(lower, URL, end) {
  var picture = "images/photos/" + URL;
	var thumb = "images/photos/thumbnails/" + URL;
	
  count--;
	
	var next = count+1;
	
  if (count <= lower) {
	  count = end;
		next = lower;
	}
	
  document.slideshow.src = "images/photos/" + URL + count + ".jpg";
	document.previous.src = thumb + (count-1) + ".jpg";
	document.next.src = thumb + next + ".jpg";
	
}