How to deal with negative number?

Hello, I’m a new user in PYNQ.
I have a problem after I followed this tutorial video (How to make a custom PYNQ overlay - YouTube).
I tried to change from positive numbers to negative numbers (change from 5,4 into -5,-4).
The result of summation should be a negative number (-9) but the result becomes the 2’s complement of -9. Can you tell me what happened and how to fix it?
Thanks for the help.