# SOI Chocolate

Note: This is not happening this year.

The Swiss Olympiad in Informatics is a great thing, but unfortunately not as well known across Switzerland as we would like. To motivate you to convince all your friends of participating in the remaining weeks, we start with a new reward system today: Each one of you who motivates a friend to participate in our first round will get a chocolate stick called “Prügeli” (also called “Brancheli” or “Schoggistängeli”) by mail.

And that’s not all! You don’t just get one Prügeli for each new participant, but also half of their Prügeli added on top of that. So if you convince someone who again convinces four more participants, you will get $1 + \frac{4}{2} = 3$ Prügeli.

And this is how our Prügeli bonus system works in detail:

What’s the exact formula to compute how many Prügeli I will get? The number of Prügeli that you earn is computed as a sum over all participants that you recruited. For each such participant, you get one Prügli plus half of the number of Prügeli that this participant gets. So the more participants you can convince of SOI, the more Prügeli you will get. And if the participants that you convinced then go on and convince even more participants, you will profit from that as well. A few examples:

• If you recruit four participants, who all don’t recruit further themselves, you get $4 \cdot 1=4$ Prügeli.
• If you recruit two participants, who in turn convince another participant each, you get $2 \cdot (1+0.5)=3$ Prügeli.
• If two participants convince each other, both of them get 2 Prügeli each.

How do you even know who told us about SOI? We simply ask all the contestants that scored points in the first round by email.

When will I get my Prügeli? As soon as someone confirms to us that she/he learned about SOI through you, we will send out the first Prügeli to you by Post. All further Prügelis will be distributed at SOI-day on January 6, 2018.

What if I convinced myself to compete at SOI? That’s great of course! Just let us know and we will send some chocolate along your way.

Isn’t this a pyramid scheme? No, not quite. One one hand it does not cost you anything - you can only win some chocolate. On the other hand, this Prügeli scheme does not bet on the number of participants to grow exponentially for it to work.

Can you guys even afford so many Prügeli? Hmm, we think so. Just think about how many Prügeli we have to buy per participant at most.

What should I do if I have any questions? We are there to help. Please write to us: chocolate@soi.ch.