input: 
  from typing import List
  
  class Sum:
      def __init__(self, x: int, y: int):
          self.x = x
          self.y = y
  
      def add(self) -> int:
          """ Return the sum of two integers x and y.
          >>> sum_instance = Sum(2, 3)
          >>> sum_instance.add()
          5
          >>> sum_instance = Sum(-1, 1)
          >>> sum_instance.add()
          0
          """
          return self.x + self.y
  
output:     
          return self.x + self.y
  