function getPageHeight(){
	var body = document.body,
		html = document.documentElement;

	var height = Math.max( body.scrollHeight, body.offsetHeight, 
		html.clientHeight, html.scrollHeight, html.offsetHeight );

	var overlay = document.getElementById('overlay'); 
	
	overlay.style.height = height + 'px'
}

function hide_div(div_name){

	if(document.getElementById(div_name).className == 'block'){
		document.getElementById(div_name).className='none'
	} else {
		document.getElementById(div_name).className='block'
	}
}

function show_div(div_name){

	if(document.getElementById(div_name).className == 'none'){
		document.getElementById(div_name).className='block'
	} else {
		document.getElementById(div_name).className='none'
	}
}