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.
          >>> s = Sum(3, 5)
          >>> s.add()
          8
          >>> s = Sum(10, -2)
          >>> s.add()
          8
          >>> s = Sum(0, 0)
          >>> s.add()
          0
          """
          return self.x + self.y
output:     return self.x + self.y