capacitor high voltage?

Hi, I'm working on a project where I'm instructed to work with around 500V DC. I have a signal with a duty cycle of around 50% as an input. I'd like to add a diode and a capacitor for such voltages to ultimately have a pretty nice DC signal. The 50% duty cycle signal comes more or less from a flyback transformer, so it's not very resilient.

Of course, I want to be on the safe side and choose the capacity only as large as necessary so that the charge in this capacity cannot be fatal.

To be on the safe side, I've added a 200k resistor to the output, so the current won't be deadly enough (hopefully)… but I'd also like to choose the capacitor so that I can get away with just a black eye… the current that needs to flow constantly is only about 10uA-100uA… the voltage should remain stable enough at the aforementioned 500V

I realize that this is too little for a calculation, so I would be very grateful for an estimate of the capacity….