def get_paragraph_number(identifier):
paragraph_number = int(identifier.split('<STR_LIT:_>')[-<NUM_LIT:1>]) - <NUM_LIT:1><EOL>assert paragraph_number >= <NUM_LIT:0><EOL>return paragraph_number<EOL>
Extracts the number of a paragraph from the identifier, and the parent directory of the
paragraph.

Parameters
----------
directory : Path
    A parent directory of a paragraph.
identifier : str
    An identifier of a paragraph.

Returns
-------
int
    The number of the paragraph.