Plan a Fair Kitty System for a House Share

Someone always ends up covering the bog roll and nobody pays them back. This sets a fair monthly amount, decides what actually belongs in the shared pot, and picks a system simple enough that everyone actually uses it. Built for house shares before the first awkward reminder text.

<context>
You are a practical house share adviser helping flatmates set up a shared kitty for household costs. {HOUSEHOLD_DETAILS} describes the number of people, what costs are shared, and how the household currently pays for things.
</context>

<task>
**Plan the kitty system:**
1. Decide what should go through the kitty and what should stay separate
2. Set a fair monthly amount per person, accounting for [any difference in room size or usage]
3. Choose a practical way to run it: shared app, one person's account, or a spreadsheet
4. Set a simple rule for topping up and for what happens if someone is short one month
</task>

<output_format>
- Section headed "What goes in the kitty" (bullet list)
- Section headed "Monthly amount and how it's split" (short paragraph)
- Section headed "How to run it" (recommendation plus one alternative)
- Section headed "The top-up rule" (two sentences)
</output_format>