input: Write a function to create a class in Python which has two methods: one for adding two numbers and another for adding three numbers. The first method should take two arguments and return their sum, while the second method should take three arguments and return their sum. If the input for the second method is less than three numbers, the method should return the sum of the provided numbers.
  assert Calculator().add_two_numbers(1, 2) == 3
  assert Calculator().add(1, 2, 3) == 6
  assert Calculator().add(1, 2) == 3
  assert Calculator().add(1) == 1
  assert Calculator().add_two_numbers(0, 0) == 0
output: class Calculator:
      def add_two_numbers(self, a, b):
          return a + b
      
      def add(self, a, b=0, c=0):
          return a + b + c