l=Math.floor(Math.random()*1000);

document.write('<br>');
switch(l % 16)
{
  case 0:
  case 1:
  case 2:
  case 3:
  case 4:
  case 5:
  case 6:
  case 7:
  case 8:
  case 9:
  case 10:
  case 11:
  case 12:
  case 13:
  case 14:
  case 15:
    document.write('<script language="javascript" src="http://www.21stars.net/top_image/ads_netjokes_468x60.js"></script>');
    break;
  default:
}
document.write('<br>');