How can I make a negative value driver for corrective shapekey

I’m making a driver for my shape key and I need to get rid of a deformity. I want my shapekey value to be 1.0 while my rotation is -1.0.

In order to reverse a number you can think of this Python code

>>> def invert_num(x):
	return 1 - x

>>> invert_num(0)
>>> invert_num(0.5)
>>> invert_num(1.0)

The real meaning is only in this line you can use as driver expression.

1.0 - PropertyName