2004 Cayley Problem 5

In the sequence, each figure is made up of small squares of side length 1. What is the outer perimeter of the fifth figure in the sequence?

\textbf{(A)}\ 9\quad \textbf{(B)}\ 18\quad \textbf{(C)}\ 20\quad \textbf{(D)}\ 24\quad \textbf{(E)}\ 36

If there are no answer choices shown, enter a numerical answer.

Full credit to this problem is given to the CEMC, you may view all Cayley contests here.