document.write('<style type="text/css" media="screen">body{background-image:url(/navigation/back_page_'+checkSize()+'.jpg);}</style>');
var currentSize = 0;
window.onresize = bResize;

function bResize() {
	var newSize = checkSize();
	if(newSize!=currentSize) {
		currentSize = newSize;
		document.getElementsByTagName('body')[0].style.backgroundImage = "url(navigation/back_page_"+currentSize+".jpg)";
	}
}

function checkSize() {
	var bWidth = 0, bHeight = 0, newSize = 0;
	if( typeof(window.innerWidth )=='number') {
		bWidth = window.innerWidth;
		bHeight = window.innerHeight;
	} else if(document.documentElement && (document.documentElement.clientWidth || document.documentElement.clientHeight)) {
		bWidth = document.documentElement.clientWidth;
		bHeight = document.documentElement.clientHeight;
	} else if(document.body && (document.body.clientWidth || document.body.clientHeight)) {
		bWidth = document.body.clientWidth;
		bHeight = document.body.clientHeight;
	}
	if(bWidth<=1100 && bHeight<=800) newSize = 1100;
	else if(bWidth<=1440 && bHeight<=1047) newSize = 1440;
	else newSize = 1600;
	return newSize;
}