var n = 2;
var num = Math.round((n-1)*Math.random())+1;
setTimeout('gira('+num+')', 12000);

function gira(id){
  for (k=1;k<=n;k++) {
	  if(k==id)
	    document.getElementById("p"+k).style.display="block";
	  else
	    document.getElementById("p"+k).style.display="none";
  }
  var num = Math.round((n-1)*Math.random())+1;
  setTimeout('gira('+num+')', 12000);
}