var how_many_ads = 3;
var now = new Date();
var sec = now.getSeconds();
var ad = sec % how_many_ads;
ad +=1;
if (ad==1) {
var msg4="<iframe src='http://www.37021.com/tom1.htm' width=468 height=63 scrolling=no marginwidth=0 marginheight=0 frameborder=0 vspace=0 hspace=0></iframe>"
document.write(msg4)
}
if (ad==2) {
var msg4="<iframe src='http://www.37021.com/tom2.htm' width=468 height=60 scrolling=no marginwidth=0 marginheight=0 frameborder=0 vspace=0 hspace=0></iframe>"
document.write(msg4)
}
if (ad==3) {
var msg4="<iframe src='http://www.37021.com/tom3.htm' width=468 height=60 scrolling=no marginwidth=0 marginheight=0 frameborder=0 vspace=0 hspace=0></iframe>"
document.write(msg4)
}