input: Write a function to define a class named Calculator in Python that implements two methods: add_two_numbers to add two numbers and add to add three numbers. The add_two_numbers method should take two arguments, a and b, and return their sum. The add method should take three arguments, a, b, and c, 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(1, 2, 3) == 6
  assert Calculator().add_two_numbers(-1, -2) == -3
  assert Calculator().add(0, 0, 0) == 0
  assert Calculator().add(10, 20, 30) == 60
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