How do you get a 3 cell currency conversion formula to be editable?

OK, I haven't been on this forum for ages and I am using Libre Calc instead but I was wondering how I could achieve this goal.

I want to create a simple 3 cell formula that does simple, singular currency conversion: First currency value, second currency value and the exchange rate.

However, I want to make it so that whichever cell I edit, the other cell values change dynamically. I understand that there is a conflict when it comes to cell input here because you can only have either a formula in a cell or have it editable and not both. Is it possible to break this rule?

If anyone has a solution, though, or can think of a workaround then I would be greatly appreciative.

Sorry if this sounds like a weird request.

Thanks for your time.

Cheers,
Paul
(mix_mash)