input: Write a function to describe a class in Python which implements two methods to add two numbers and another method to add three numbers. The first method, `add_two_numbers`, should take two inputs and return their sum. The second method, `add`, should take three inputs and return their sum. The class name should be `Calculator`.
  
  assert Calculator().add_two_numbers(1, 2) == 3
  assert Calculator().add(1, 2, 3) == 6
  assert Calculator().add_two_numbers(5, 7) == 12
  assert Calculator().add(10, 20, 30) == 60
  assert Calculator().add_two_numbers(-1, -1) == -2
  assert Calculator().add(0, 0, 0) == 0
output: class Calculator:
      def add_two_numbers(self, a, b):
          return a + b
      
      def add(self, a, b, c):
          return a + b + c