In any language, certain combinations of letters do not appear (or at least appear so seldom that they can be considered non-existent). For instance, there are no English words contain-ing
the three letter combination buv as a substring. Given a list of letter combinations that do
not exist, the number of possible “words” in a language can be reduced a lot (a “word” here
means any combination of letters that doesn’t contain any of the given letter combinations
as a substring). If we order all such words by increasing length, ordering words of the same
length alphabetically, we can enumerate them starting from 1. Assume that the alphabet
always consists of the lower case letters ’a’ to ’z’.

For instance, if the list only contains the combinations q, ab and aaa, the words would be
enumerated like this:

  1.  a
  2.  b
   
 16.  p
 17.  r
   
 26.  aa
 27.  ac
   

649.  zz
650.  aac

Given the list of letter combinations, write a program that for a given word outputs its
number, and for a given number ouputs its word. You can assume that none of the words
will exceed 20 characters and no number will be greater than 2 000 000 000 (for both input
and output).