input: Write a function to implement a Calculator class in Python that contains methods to add two numbers and three numbers. The `add_two_numbers` method should take two integers as input and return their sum. The `add` method should take three integers as input and return their sum.
  
  
  class Calculator:
      def __init__(self):
          pass
      
      def add_two_numbers(self, a, b):
          return a + b
  
      def add(self, a, b, c):
          return a + b + c
  
  assert Calculator().add_two_numbers(1, 2) == 3
  assert Calculator().add_two_numbers(0, 0) == 0
  assert Calculator().add_two_numbers(-1, 1) == 0
  assert Calculator().add(1, 2, 3) == 6
  assert Calculator().add(0, 0, 0) == 0
  assert Calculator().add(-1, 1, 0) == 0
  
output: class Calculator:
      def __init__(self):
          pass
      
      def add_two_numbers(self, a, b):
          return a + b
  
      def add(self, a, b, c):
          return a + b + c