layer=new Array("l01","l02","l03","l04");
var i=0,tid;
var n=layer.length;

function next(num){

	stop();
	tid=setInterval("next();",10000);
	
	if(num) {
		i = num - 2;
	}
	
	if(i < n -1){
		i++;change();
	}else{
		i=0;change();
	}
}

function stop(){
	clearInterval(tid);
}

function change(){
	
	for (var s=0;s<n;s++)
	{
		document.getElementById(layer[s]).style.display= "none";
	}
	
	document.getElementById(layer[i]).style.display= "block";

}