I've noticed that the add or subtract button is still there after finishing the final math problem, and when you keep adding or subtracting, you get stuck on a page that just says
"final code= 5+3=7
final code= 5+3=7"
Otherwise the concept of this is very interesting and fun! I found the puzzles to be very simple and it made me wish I felt more of a sense of urgency when completing the puzzles.