Official Ruby Inspector Here is a simple ASCII art ruby:
  ___
 /\_/\
/_/ \_\
\ \_/ /
 \/_\/

As a jeweler for the ASCII Gemstone Corporation, your job is inspect the newly acquired rubies and leave a note about any defects that you find.
Luckily, only 12 types of defects are possible, and your supplier guarantees that no ruby will have more than one defect.
The 12 defects correspond to the replacement of one of the 12 inner _, /, or \ characters of the ruby with a space character ( ). The outer perimeter of a ruby never has defects.
The defects are numbered according to which inner character has a space in its place:

So a ruby with defect 1 looks like this:
  ___
 /\_/\
/_/  _\
\ \_/ /
 \/_\/

A ruby with defect 11 looks like this:
  ___
 /\_/\
/_/ \_\
\ \_/ /
 \ _\/

It's the same idea for all other defects.
Challenge
Write a program or function that takes in the string of a single, potentially defective ruby. The defect number should be printed or returned. The defect number is 0 if there is no defect.
Take input from a text file, stdin, or a string function argument. Return the defect number or print it to stdout.
You may assume that the ruby has a trailing newline. You may not assume that it has any trailing spaces or leading newlines.
The shortest code in bytes wins. (Handy byte counter.)
Test Cases
The 13 exact types of rubies, followed directly by their expected output:
  ___
 /\_/\
/_/ \_\
\ \_/ /
 \/_\/
0
  ___
 /\_/\
/_/  _\
\ \_/ /
 \/_\/
1
  ___
 /\ /\
/_/ \_\
\ \_/ /
 \/_\/
2
  ___
 /\_/\
/_  \_\
\ \_/ /
 \/_\/
3
  ___
 /\_/\
/_/ \_\
\  _/ /
 \/_\/
4
  ___
 /\_/\
/_/ \_\
\ \ / /
 \/_\/
5
  ___
 /\_/\
/_/ \_\
\ \_  /
 \/_\/
6
  ___
 /\_/\
/_/ \ \
\ \_/ /
 \/_\/
7
  ___
 /\_ \
/_/ \_\
\ \_/ /
 \/_\/
8
  ___
 / _/\
/_/ \_\
\ \_/ /
 \/_\/
9
  ___
 /\_/\
/ / \_\
\ \_/ /
 \/_\/
10
  ___
 /\_/\
/_/ \_\
\ \_/ /
 \ _\/
11
  ___
 /\_/\
/_/ \_\
\ \_/ /
 \/_ /
12
Ruby 2.0, 69 bytes

#!ruby -Kn0rdigest
p'&#xd7;&#xf1;F&lt;&#x1f;&#xec;X&#x82;&#xc9;&#xb2;&#x9f;_&#x2;'.index Digest::MD5.digest(gets)[0]


Hexdump (to faithfully show the binary data in the string):

00000000  23 21 72 75 62 79 20 2d  4b 6e 30 72 64 69 67 65  |#!ruby -Kn0rdige|
00000010  73 74 0a 70 27 d7 f1 46  3c 1f ec 58 82 c9 b2 9f  |st.p'..F&lt;..X....|
00000020  5f 02 27 2e 69 6e 64 65  78 20 44 69 67 65 73 74  |_.'.index Digest|
00000030  3a 3a 4d 44 35 2e 64 69  67 65 73 74 28 67 65 74  |::MD5.digest(get|
00000040  73 29 5b 30 5d                                    |s)[0]|


Explanation:


The -Kn option reads the source file as ASCII-8BIT (binary).
The -0 option allows gets to read in the whole input (and not just one line).
The -rdigest option loads the digest module, which provides Digest::MD5.
The code then does an MD5 of the input, takes the first byte of the digest, and gets its index in the given binary string.