my skills: C/C++,HTML,CSS,Dreamweaver,Photoshop,Illustrator,Coral Draw,PHP

i want to know how much ruby should i learn to grasp rails?

i am having all the pdf of the books. Ruby itself is very much vast. so i want to know that for learning rails,should i go through each topic of Ruby?

In Pragmatic Agile Web Development with Rails 4th Edition, Ruby is introduced in 12pages only & in other books its 500+. please advice me what should i do.