var imgWidth=120;
function moveToPrevious()
{
  	var left = getLeft($('imageBoxInside'));
	if (left < -imgWidth*0.9) {
		new Effect.Move('imageBoxInside', {
			x: imgWidth,
			y: 0,
			transition: Effect.Transitions.sinoidal
		});
	}
	else if(left!=0){		
		new Effect.Move('imageBoxInside', {
			x: -left,
			y: 0,
			transition: Effect.Transitions.sinoidal
		});
	}
} 
function getLeft(element){
	var left = element.getStyle('left');
	return (left==null) ? 0 : left.substring(0, left.length-2);	
}
function moveToNext()
{
	var imageBoxInside = $('imageBoxInside');
	var imageBox = $('imageBox');
	var children = imageBoxInside.descendants();
  	var left = getLeft(imageBoxInside);
	var minLeft = (children.length/2 + 1 - Math.ceil(imageBox.getWidth()/imgWidth)) * -imgWidth;
	if (left > minLeft) {
		new Effect.Move('imageBoxInside', {
			x: -imgWidth,
			y: 0,
			transition: Effect.Transitions.sinoidal
		});
	}
	else{		
		new Effect.Move('imageBoxInside', {
			x: minLeft-left,
			y: 0,
			transition: Effect.Transitions.sinoidal
		});
	}
}