"""File:     to_roman2a.py
   Purpose:  Convert a single character Roman numeral into a Hindu-Arabic
             numeral.  Print a message if the character entered by the
             user isn't a legal Roman numeral, and exit.

   Run:      python to_roman2a.py

   Input:    Single character of a Roman numeral
   Output:   Corresponding Hindu-Arabic numeral or error message
"""

from sys import exit

#----------------------------------------------------------------------
def convert_to_number(roman_sym):
   """Convert a single character Roman numeral into a number
   """
   if roman_sym == 'M':
      return 1000
   elif roman_sym == 'D':
      return 500
   elif roman_sym == 'C':
      return 100
   elif roman_sym == 'L':
      return 50
   elif roman_sym == 'X':
      return 10
   elif roman_sym == 'V':
      return 5
   elif roman_sym == 'I':
      return 1
   else: 
      print roman_sym, "isn't a valid Roman numeral!"
      exit()

#----------------------------------------------------------------------
# Program starts here
roman = raw_input("Enter a single character Roman numeral\n")
number = convert_to_number(roman)
print "The Roman numeral", roman, "corresponds to the"
print "    Hindu-Arabic numeral", number