if my program is free, do i still have to buy ckeditor?

As the title says, i want to create a website CMS and have ckeditor as my editor.
Now my program will be free, BUT not open source, for i want to retain the copywrite on my source code.

I have read the Open source license that ckeditor uses, but i am still confused on what exactly i can, and can not do.

I want to be able to use ckeditor in my program, and release my program free of charge, so do i still need to buy the ckeditor license?

And if i have to buy it, what open source license will allow me to retain my copywrite but allow modifications, etc..

Thanks!