text: # -*- coding: utf-8 -*-
  """Main module."""
  
  
  class MutableNumber:
      def __init__(self, number):
          self.history = [number]
  
      def get(self, idx=-1):
          return self.history[idx]
  
      def add(self, addend):
          number = self.get() + addend
          self.history.append(number)
          return self
  
      def subtract(self, subtrahend):
          number = self.get() - subtrahend
          self.history.append(number)
          return self
  
      def multiply(self, factor):
          number = self.get() * factor
          self.history.append(number)
          return self
  
      def divide(self, divisor):
          number = self.get() / divisor
          self.history.append(number)
          return self
  