# -*- coding: utf-8 -*-
# Let's try making a custom exception.
# Usage: python 21.py number
# It will throw an error if the number is non hexadecimal

import sys, string

class NonHexException(Exception):
  pass

def printHexNumber(hexString):
  hexDigits = string.hexdigits
  for c in theString:
    if not c in hexDigits:
      raise NonHexException("Not a hexadecimal number")
  print hexString

theString = sys.argv[1]

try:
  printHexNumber(theString)
except NonHexException:
  print "Error: this is not a hexadecimal number"