input: class MedianFinder:
      def __init__(self):
          self._data = []
      
      def add(self, num):
          self._data.append(num)
      
      def find_median(self):
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2])/2
  
  """Find the median of an unsorted list of numbers by adding numbers to a list and then sorting it to find the median.
  Example:
  >>> median_finder = MedianFinder()
  >>> median_finder.add(3)
  >>> median_finder.add(1)
  >>> median_finder.add(5)
  >>> median_finder.add(4)
  >>> median_finder.find_median()
  3.0
  """
output:     
  class MedianFinder:
      def __init__(self):
          self._data = []
      
      def add(self, num):
          self._data.append(num)
      
      def find_median(self):
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2])/2
  