var cur_ad = 1;
var nxt_ad = 1;
var timeoutId;

function switch_ad(l){
	document.getElementById('sel_1').className = "selector";
	document.getElementById('sel_2').className = "selector";
	document.getElementById('sel_3').className = "selector";
	document.getElementById(l).className = "selector_active";
	
	clearTimeout(timeoutId);
	timeoutId = setTimeout(next_ad, 10000);
	
	switch(l){
		
		case "sel_1":
		document.getElementById('ad_1').style.display = "block";
		document.getElementById('ad_2').style.display = "none";
		document.getElementById('ad_3').style.display = "none";
		cur_ad = 1;
		nxt_ad = 1;
		break;
		
		case "sel_2":
		document.getElementById('ad_1').style.display = "none";
		document.getElementById('ad_2').style.display = "block";
		document.getElementById('ad_3').style.display = "none";
		cur_ad = 2;
		nxt_ad = 2;
		break;
		
		case "sel_3":
		document.getElementById('ad_1').style.display = "none";
		document.getElementById('ad_2').style.display = "none";
		document.getElementById('ad_3').style.display = "block";
		cur_ad = 3;
		nxt_ad = 3;
		break;
		
		default:
		document.getElementById('ad_1').style.display = "block";
		document.getElementById('ad_2').style.display = "none";
		document.getElementById('ad_3').style.display = "none";
		cur_ad = 1;
		nxt_ad = 1;
	
	}
	
}

function next_ad(){
	
	if(cur_ad == 3){
		nxt_ad = 1;
	}
	else{
		nxt_ad++;	
	}
	
	switch_ad("sel_"+nxt_ad);
	
	clearTimeout(timeoutId);
	
	timeoutId = setTimeout(next_ad, 10000);
	
}

timeoutId = setTimeout(next_ad, 10000);