function escolheIMG() {
	var randomnumber=Math.floor(Math.random()*3);
	//alert(randomnumber);
	if (randomnumber==0){	
		document.getElementById("portal-top").style.backgroundImage = "url(topo_bg0)";
	}
	if (randomnumber==1){	
		document.getElementById("portal-top").style.backgroundImage = "url(topo_bg1)";
	}
	if (randomnumber==2){	
		document.getElementById("portal-top").style.backgroundImage = "url(topo_bg2)";
	}
}