Hack the Box - Deceitful Batman Challenge

This text appeared on a Batman show but we suspect that it is actually code. It’s your job to find out what it says! (The flag is in uppercase)

This is what we have inside finale.txt

NAANAAANNNAANAAAANANANANAAAAAAAANNAANAAANAAANANNAAAAAAAANNNAANAAAAANAANAAAA

You’ll get this:

THEFLAGISNAPIER