I have a disk for Photoshop CS5, but I can't find the serial number in order to install. Where can I find it?

I recently purchased a new computer. I had Photoshop installed on the previous one, which is outdated and will no longer be used.

I still have the disc that was used to load the program on that computer, but I do not have the serial number.

Is there a way to get the serial number so I can officially install the program?

I had it stored in a box, but the box was for Elements 5.0, so the serial number is incorrect.