Does anyone have an idea why isn’t it working??

Question

Help me I can’t get a hack why it gives NaN...
https://code.sololearn.com/WgkZsYQ9KIFy/?ref=app

Answer 1

Change all =+ to +=

Answer 2

Only if you didn't understood what @anna said.
https://code.sololearn.com/WkZU2vQ6Ku66/?ref=app

Answer 3

Thank you so much guys!