input: Write a function to create a class named `Calculator` with two methods: `add_two_numbers` which takes two arguments and returns their sum, and `add` which takes three arguments and returns their sum. The class should initialize without any specific attributes.
  
  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(1, 2, 3) == 6
  assert Calculator().add_two_numbers(-1, 1) == 0
  assert Calculator().add(0, 0, 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