input: Write a function to implement a class in Python that has two methods to add two numbers and three numbers respectively. The class should be named Calculator. If no numbers are provided, the methods should return 0.
  assert Calculator().add_two_numbers(1, 2)==3
  assert Calculator().add(1, 2, 3)==6
  assert Calculator().add_two_numbers(0, 0)==0
  assert Calculator().add(0, 0, 0)==0
output: class Calculator:
      def add_two_numbers(self, a=0, b=0):
          return a + b
      
      def add(self, a=0, b=0, c=0):
          return a + b + c