input: Write a function to implement a class named Calculator with two methods to add two numbers and three numbers respectively. The add_two_numbers method should take two arguments and return their sum. The add method should take three arguments and return their sum. If the given arguments are not numbers, return "Invalid input".
  class Calculator:
      def __init__(self):
          pass
      
      def add_two_numbers(self, a, b):
          if isinstance(a, (int, float)) and isinstance(b, (int, float)):
              return a + b
          else:
              return "Invalid input"
      
      def add(self, a, b, c):
          if isinstance(a, (int, float)) and isinstance(b, (int, float)) and isinstance(c, (int, float)):
              return a + b + c
          else:
              return "Invalid input"
  
  calculator = Calculator()
  assert calculator.add_two_numbers(1, 2)==3
  assert calculator.add_two_numbers(3.5, 2.5)==6.0
  assert calculator.add_two_numbers("3", 2)=="Invalid input"
  assert calculator.add(1, 2, 3)==6
  assert calculator.add(1.5, 2.5, 3.5)==7.5
  assert calculator.add(1, "2", 3)=="Invalid input"
output: def add_two_numbers(self, a, b):
      if isinstance(a, (int, float)) and isinstance(b, (int, float)):
          return a + b
      else:
          return "Invalid input"
  
  def add(self, a, b, c):
      if isinstance(a, (int, float)) and isinstance(b, (int, float)) and isinstance(c, (int, float)):
          return a + b + c
      else:
          return "Invalid input"