Thank you very much DJ Omnimaga
I'd like to add something about the difficulty of the game: some levels are extremely difficult, and some can even seem impossible. If you're completely stuck on a level, sometimes the best thing to do is stop playing it for a while and only retry it after a few weeks, or even a few months. If you still can't manage to beat a level after that, you may want to wait again, until the 1st of April this time, and retry the level then (in that case, make sure your calculator's date is correctly set - you can see it and set it in the [mode] menu). All the levels are easier on that day.
I'd like to add something about the difficulty of the game: some levels are extremely difficult, and some can even seem impossible. If you're completely stuck on a level, sometimes the best thing to do is stop playing it for a while and only retry it after a few weeks, or even a few months. If you still can't manage to beat a level after that, you may want to wait again, until the 1st of April this time, and retry the level then (in that case, make sure your calculator's date is correctly set - you can see it and set it in the [mode] menu). All the levels are easier on that day.