Is CCNA: Security standalone or does it build off CCNA?

I've never taken a Cisco exam before but I'm looking to get into them. Since my job and career focus is primarily security minded I was going to go straight for CCNA: Security, but the book for the exam is very thin and the books for the regular CCNA are thick as tree trunks and so I was wondering if the CCNA: Security was a standalone exam or if it assumes knowledge of CCNA material.

Basically the question is, can you take CCNA: Security by itself or is the intention that one takes CCNA first, then the security exam is like an amendment to it?