String.prototype.left = function left(n)
{
	if (n <= 0) return "";
	else if (n > this.length) return this;
	else return this.substring(0,n);
}

String.prototype.right = function right(n)
{
	if (n <= 0) return "";
	else if (n > this.length) return this;
	else return this.substring(this.length, this.length - n);
}

function checkScroll(menuID)
{
	mainObj = document.getElementById("mainContainer");
	menuObj = document.getElementById(menuID);
	
	var differ = mainObj.scrollTop;
	var menuMarginTop = menuObj.style.marginTop;
	
	if (differ > 0) menuMarginTop = -40 + differ;	
	else menuMarginTop = -40;
	
	menuObj.style.marginTop = menuMarginTop + "px";	
}