code: def convert_to_G(self, word):
      
      value = 0.0
      if word[-1] == 'G' or word[-1] == 'g':
        value = float(word[:-1])
      elif word[-1] == 'M' or word[-1] == 'm':
        value = float(word[:-1]) / 1000.0
      elif word[-1] == 'K' or word[-1] == 'k':
        value = float(word[:-1]) / 1000.0 / 1000.0
      else:  # No unit
        value = float(word) / 1000.0 / 1000.0 / 1000.0
      return str(value)
docs: Given a size such as '2333M', return the converted value in G