Calculator User Story #13: Subsequent Negative Operator in Consecutive Input

I managed to pass 15/16 User Stories. However, I am reluctant to incorporate User Story # 13 within my app as I have already incorporated +/- button to change the integer’s +/- value. I’d rather think that if I incorporate that user story, it creates a redundancy to the detriment of the user (instead of their benefit), since from the onset I took an Explicit approach rather than Implicit (+/- change within the subtract button).

It’s not that I cannot do that, I just think that design-wise, it down-grade my app by compromising consistency in what the button (expected to) performs.

What do you think? Can I just submit this as done? Thank you.
Link to my calculator as follows:

13. If 2 or more operators are entered consecutively, the operation performed should be the last operator entered (excluding the negative (-) sign.
The sequence "5 * - 5" = should produce an output of "-25" : expected '0' to equal '-25'
AssertionError: The sequence "5 * - 5" = should produce an output of "-25" : expected '0' to equal '-25'