input: from typing import List
  
  class MedianFinder:
      def __init__(self):
          self._data = []
      
      def add(self, num: float):
          self._data.append(num)
      
      def find_median(self) -> float:
          """ Finds the median of the unsorted list of numbers.
          >>> median_finder = MedianFinder()
          >>> median_finder.add(3)
          >>> median_finder.add(1)
          >>> median_finder.add(2)
          >>> median_finder.find_median()
          2.0
          >>> median_finder.add(4)
          >>> median_finder.find_median()
          2.5
          """
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2]) / 2
output:     
          data = sorted(self._data)
          n = len(data)
          return (data[(n-1)//2] + data[n//2]) / 2
  