var how_many_ads = 5;
var now = new Date()
var sec = now.getSeconds()
var ad = sec % how_many_ads;
ad +=1;
// if (ad==number) {
//txt="This is a blank example. Be sure to end the entry with a period.";
//url="Enter the link this should go to";
//alt="Enter alt text that loads in case the image doesn't";
//image="Enter the link to the image. Then you're finished!";
//}
if (ad==1) {
alt="Physics";
image="images/cover-1.jpg";
}
if (ad==2) {
alt="English";
image="images/cover-2.jpg";
}
if (ad==3) {
alt="English";
image="images/cover-3.jpg";
}
if (ad==4) {
alt="English";
image="images/cover-4.jpg";
}
if (ad==5) {
alt="English";
image="images/cover-5.jpg";
}
document.write('<center>');
document.write('<img src=\"' + image + '\"'); 
// width=');
document.write('border=\"0\"');
//document.write('width=\"20\" height=\"75\" align=\"BOTTOM\" border=\"0\" natu$
document.write('alt=\"' + alt + '\"></a><br>');
//document.write(width + ' height=' + height + ' ');  
//document.write('alt=\"' + alt + '\" border=0><br>');
document.write('</center>');
// -->