Task 3 Negative numbers clarification

[SaberDoTcodeR]

Hi, I think Task 3 needs a bit of clarification.

First of all is this a possible input? "-1*-2"

Also, how should we encode the negative result? By representing the exact string of the result: -ABCD

PS: My submission has 3 out of 10 passes, so I guess it might be negative numbers.