var num = 0;
	setInterval(function(){ 
		if(num == 0) {
			num = 1;
			document.getElementById('ban_0').style.display="none";
			document.getElementById('ban_1').style.display="block";
		}else{
			num = 0;
			document.getElementById('ban_0').style.display="block";
			document.getElementById('ban_1').style.display="none";
		}
	},20000);