var rand1 = Math.random();
var rn1 = Math.floor(rand1*100+1);
 
<!-- TD Server 728x90
if(rn1>=50 && rn1<=99) 
{
var uri = 'http://impes.tradedoubler.com/imp?type(js)pool(92545)a(914690)' + new String (Math.random()).substring (2, 11);
document.write('<sc'+'ript type="text/javascript" src="'+uri+'" charset="ISO-8859-1"></sc'+'ript>');
}

<!-- Netfilia
if(rn1>=0 && rn1<50) 
{
google_ad_client = "pub-6218180040187539";
/* Webtrucos 728x90 */
google_ad_slot = "0799858846";
google_ad_width = 728;
google_ad_height = 90;
document.write('<script type="text/javascript" src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>');
}