1 #!/usr/bin/env python

     2 import re

     3 import sys

     4 

     5 cn = sys.argv[1]

     6 

     7 r1 = '((a?){%s})' % cn

     8 r2 = 'a{%s}' % cn

     9 

    10 m = re.match(r1 + r2 , "a" * int(cn)) 

    11 

    12 print m.group(0)