Convert peano number s(N) to integer in Prolog

Question

I came across this natural number evaluation of logical numbers in a tutorial and it's been giving me some headache:

natural_number(0).
natural_number(s(N)) :- natural_number(N).

The rule roughly states that: if N is 0 it's natural, if not we try to send the contents of s/1 back recursively to the rule until the content is 0, then it's a natural number if not then it's not.

So I tested the above logic implementation, thought to myself, well this works if I want to represent s(0) as 1 and s(s(0)) as 2, but I´d like to be able to convert s(0) to 1 instead.

I´ve thought of the base rule:

sToInt(0,0). %sToInt(X,Y) Where X=s(N) and Y=integer of X

So here is my question: How can I convert s(0) to 1 and s(s(0)) to 2?

Has been answered

Edit: I modified the base rule in the implementation which the answer I accepted pointed me towards:

decode(0,0). %was orignally decode(z,0).
decode(s(N),D):- decode(N,E), D is E +1.

encode(0,0). %was orignally encode(0,z).
encode(D,s(N)):- D > 0, E is D-1, encode(E,N).

So I can now use it like I wanted to, thanks everyone!