I'll name that tune in 3...
pps, part of reading music is context, meaning we look at a larger part of the music. The way you gave us just a few notes suggests you're not thinking in that way yet.I don't know what the piece is but I'm already guessing that this is the start of a chromatic scale and that the next note is Ab if that continues. Also, even if there are there is an Ab in the key signature, music contains notes that are not in the key signature. If it does continue down chromatically, then Anat followed by Ab would be awkward.
Why is A nat followed by A flat awkward? This would be the descending chromatic scale with the suggested fingering of ‘5’ on A nat so that ‘4’ available to play A flat.
You have three descending chromatic notes in the middle of a piece. Isn't it likely that many pieces have three chromatic notes?
What are the other clues from three notes, that make those three notes be part of this, and only this, piece?How does that knowledge help the asker know that Bbb is played using the piano key designated for Anat - or rather, would one need such knowledge to figure that out? It's sort of like saying to know how to pronounced "cat", you have to first read the Dr. Seuss book.