input: 
  class Sum:
      def __init__(self, x, y):
          self.x = x
          self.y = y
          
      def add(self):
          return self.x + self.y
  
  """
  Complete the Python class that can calculate the sum of two integers.
  >>> s = Sum(3, 5)
  >>> s.add()
  8
  >>> s = Sum(-1, 2)
  >>> s.add()
  1
  """
  
output:     
      def __init__(self, x, y):
          self.x = x
          self.y = y
          
      def add(self):
          return self.x + self.y
  