input: Write a python function to create an instance of the Foo class, set its public and private variables, and access its public method.
  assert create_and_access_foo(10, 20) == 20
  assert create_and_access_foo('private', 'public') == 'public'
  assert create_and_access_foo(100, 200) == 200
output: class Foo:
      def __init__(self):
          self.public_var = None
          self.__private_var = None
      
      def public_method(self):
          return self.__private_var
  
  def create_and_access_foo(public_value, private_value):
      foo_instance = Foo()
      foo_instance.public_var = public_value
      foo_instance._Foo__private_var = private_value
      return foo_instance.public_method()