function getBG(x){
	if(x < 800){
		document.body.background = "/img/index/underwater5.jpg";
	}else if(x == 800){ 
		document.body.background = "/img/index/underwater5.jpg";
	}else if((x > 800 && x < 1024) || x == 1024){
		document.body.background = "/img/index/underwater4.jpg";
	}else if((x > 1024 && x < 1280) || x == 1280){
		document.body.background = "/img/index/underwater3.jpg";
	}else if((x > 1280 && x < 1600) || x == 1600){
		document.body.background = "/img/index/underwater2.jpg";
	}else if(x > 1600){
		document.body.background = "/img/index/underwater1.jpg"
	}
}