code: 
  """simple docstring"""
  def     __lowerCamelCase  (		UpperCamelCase__      ):
  
  
  	"""simple docstring"""
  
  
  
  
  
  
  	if not isinstance(UpperCamelCase__				,     UpperCamelCase__      ):
  		raise ValueError("double_factorial() only accepts integral values"      )
  	if n < 0:
  		raise ValueError("double_factorial() not defined for negative values"      )
  	return 1 if n <= 1 else n * double_factorial(n - 2      )
  
  
  if __name__ == "__main__":
  			import doctest
  
  			doctest.testmod()
  
  
  
  
  
style_context: 
  """simple docstring"""
  def     __lowerCamelCase  (		UpperCamelCase__ = 400_0000      ):
  
  
  	"""simple docstring"""
  
  
  
  
  
  
  	_UpperCAmelCase =						1
  	_UpperCAmelCase =						2
  	_UpperCAmelCase =						0
  	while j <= n:
  		if j % 2 == 0:
  			total += j
  		_UpperCAmelCase ,      _UpperCAmelCase =						j, i + j
  
  	return total
  
  
  if __name__ == "__main__":
  			print(f'''{solution() = }''')
  
  
  
  
  