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 msg1="<center><iframe src='http://www.amazon.cn/union/asso_easy.asp?e=5&source=w-90001866' width='468' height='60' scrolling='no' marginwidth='0' marginheight='0' frameborder='0'></iframe></center>"
document.write(msg1)
}
if (ad==2) {
var msg1="<center><iframe src='http://www.amazon.cn/union/asso_easy.asp?e=5&source=w-90001866' width='468' height='60' scrolling='no' marginwidth='0' marginheight='0' frameborder='0'></iframe>"
document.write(msg1)
}
if (ad==3) {
var msg1="<center><iframe src='http://www.amazon.cn/union/asso_easy.asp?e=5&source=w-90001866' width='468' height='60' scrolling='no' marginwidth='0' marginheight='0' frameborder='0'></iframe>"
document.write(msg1)
}