def to_dec(alphabet, number):
  """
  alphabet - string of all letters in ascending order
  number - string number to convert
  return - decimal (int) number
  """
  result = -1
  for i, v in enumerate(number):
    result += (alphabet.index(v) + 1) * len(alphabet) ** i
  return result

if __name__ == '__main__':
    # smoke test
    from string import ascii_uppercase
    assert to_dec(ascii_uppercase, 'AA') == 26