var arr = new Array();
arr[0]='img_main01.jpg';
arr[1]='img_main02.jpg';
arr[2]='img_main03.jpg';
arr[3]='img_main04.jpg';
exd = new Date();
var month = exd.getMonth();
if(month>=2 && month<=4)
	{	
		$(function(){
			$('p.mainimg').css({backgroundImage: 'url(images/' + arr[0] + ')'});
		});
	}
if(month>=5 && month<=7)
	{	
		$(function(){
			$('p.mainimg').css({backgroundImage: 'url(images/' + arr[1] + ')'});
		});
	}

if(month>=8 && month<=10)
	{	
		$(function(){
			$('p.mainimg').css({backgroundImage: 'url(images/' + arr[2] + ')'});
		});
	}

if(month>=11 || month>=0 && month<=1)
	{	
		$(function(){
			$('p.mainimg').css({backgroundImage: 'url(images/' + arr[3] + ')'});
		});
	}