input: 
  from typing import List
  
  class Sum:
      def __init__(self, x: int, y: int):
          self.x = x
          self.y = y
          
      def add(self) -> int:
          """Calculate the sum of two integers.
          >>> Sum(3, 5).add()
          8
          >>> Sum(-1, 1).add()
          0
          """
          return self.x + self.y
  
output:     
          return self.x + self.y
  