input: Write a function to create a class named Calculator with two methods: add_two_numbers which takes two parameters a and b and returns their sum, and add which takes three parameters a, b, and c and returns 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
  
  calculator = Calculator()
  assert calculator.add_two_numbers(1, 2) == 3
  assert calculator.add(1, 2, 3) == 6
  assert calculator.add_two_numbers(-1, -1) == -2
  assert calculator.add(0, 0, 0) == 0
  assert calculator.add_two_numbers(0, -1) == -1
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