#!/usr/bin/env python

import re

import sys

# case of catastrophic backtracking in Python

#

# regex: (a*)*b

# strings: aa...a

#

# call with timing as:

#

#   > time ./catastrophic.py 20

# counter n given on the command line

cn = sys.argv[1]

# calling the matching function

m = re.match('(a*)*b' , "a" * int(cn)) 

print m.group(0)