How do I write a markov algorithm to convert unary numbers to decimal?

I want to write a Markov algorithm that converts numbers such as ||| (3) ||||| (5) and so on into, decimal numbers

So I'm studying algorithms for fun and I came over this problem . The tasks says to do it with numbers 1 - 10.  It is pretty easy, but what about bigger ones (like 3000 and so on, for example). This probably doesn't have any practical use, but I really wanna know how it is done

What I have tried:

I've done it for 1-9, but can't get the idea for bigger numbers