num_pages = 0;
active_page = 0;

function set_nav() {
	if(num_pages != 0) {
		$("nav-sx").style.left = (active_page == 0) ? "-950px" : "950px";
		$("nav-dx").style.left = (active_page == num_pages-1) ? "-970px" : "970px";
	}
}

function hide_nav() {
	$("nav-sx").style.left = "-950px";
	$("nav-dx").style.left = "-970px";
}

function nav_sx_clicked() {
	hide_nav();
	new Effect.Move("inner-all", {x:472,y:0,duration:0.5, afterFinish:set_nav});
	active_page--;
}

function nav_dx_clicked() {
	hide_nav();
	new Effect.Move("inner-all", {x:-472,y:0,duration:0.5, afterFinish:set_nav});
	active_page++;
}

function set_nav_and_width() {
	num_pages = Math.ceil( $$(".white-preview-box").length / 2);
	$("inner-all").style.width = (num_pages * 472 + 10) + "px"; //+10 per sicurezza
	set_nav();
	Event.observe($("nav-sx"), 'click', nav_sx_clicked);
	Event.observe($("nav-dx"), 'click', nav_dx_clicked);
}

Event.observe(window, 'load', set_nav_and_width);