input: Write a function to implement a class in Python which has two methods to add two numbers. One method should add two numbers and the other method should add three numbers.
  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)==1
  assert Calculator().add(0, -1, 1)==0
  assert Calculator().add_two_numbers(0, 0)==0
output: def __init__(self):
      pass
      
  def add_two_numbers(self, a, b):
      return a + b
  
  def add(self, a, b, c):
      return a + b + c