function changeSizeBigger(elem)
	{
    var element = document.getElementById(elem);
	var height = parseInt(element.style.height);
	element.style.height=height+100+"px";
	}
function changeSizeSmaller(elem)
	{
    var element = document.getElementById(elem);
	var height = parseInt(element.style.height);
	if (height>=500)
		{
		element.style.height=height-100+"px";
		}
	}