input: Write a function to use the Calculator class to add two numbers and three numbers.
  assert calculator.add_two_numbers(1, 2) == 3
  assert calculator.add_two_numbers(10, 20) == 30
  assert calculator.add(1, 2, 3) == 6
  assert calculator.add(10, 20, 30) == 60
output: class Calculator:
      def add_two_numbers(self, a, b):
          return a + b
  
      def add(self, a, b, c):
          return a + b + c
  
  calculator = Calculator()