#!/usr/bin/python

class Error(Exception): pass
class NegativeNumberError: pass

class Number:
   def __init__(self, n):
      if n < 0: raise NegativeNumberError
      self.number = n
   def __add__(self, n):
      return Number(self.number+n.number)
   def __mul__(self, n):
      return Number(self.number*n.number)
   def __ne__(self, n):
      return self.number!=n.number
   def __eq__(self, n):
      return self.number==n.number
   def __repr__(self):
      return str(self.number)

if __name__ == "__main__":
   try:
      m = Number(7)
      n = Number(9)
      print m+n 
      print m*n 
      print Number(-1)
   except NegativeNumberError:
      print "Negative numbers are not allowed!"
   except:
      print "Oops, I didn't catch that!"