var margin_top = 0;
	function up(){
		margin_top = margin_top + 40;
		if (margin_top > 0) margin_top = 0;
		document.getElementById('a1').style.margin = margin_top+'px 0 0 0';
	}
	function dn(){
		margin_top = margin_top - 40;
		if (margin_top < -1300) margin_top = -1300;
		document.getElementById('a1').style.margin = margin_top+'px 0 0 0';
	}