function $(e) { return document.getElementById(e); }
function changeBg(){
	var no = Math.floor(Math.random() * 4) ;
	
	var imgArr = new Array;
	imgArr[0] = new Array('main_image1.jpg','btn_main_1a.jpg','btn_main_1b.jpg');
	imgArr[1] = new Array('main_image2.jpg','btn_main_2a.jpg','btn_main_2b.jpg');
	imgArr[2] = new Array('main_image3.jpg','btn_main_3a.jpg','btn_main_3b.jpg');
	imgArr[3] = new Array('main_image4.jpg','btn_main_4a.jpg','btn_main_4b.jpg');
	
	$('mainImg').style.backgroundImage = "url('img/" + imgArr[no][0] + "')";
	$('btnMain01').style.backgroundImage = "url('img/" + imgArr[no][1] + "')";
	$('btnMain02').style.backgroundImage = "url('img/" + imgArr[no][2] + "')";
	
	$('btnMain01').style.backgroundRepeat = 'no-repeat';
	$('btnMain02').style.backgroundRepeat = 'no-repeat';
}
window.onload = function(){
	//changeBg();
}