Here is my stab at the logic, derived from giyam's answers below and Googling set notation:

Give me the set of x such that for all y in set(x) and set(y) is a function of (where) y <= x

However, I think the italicized section above is unclear due to the nature of the problem as it is written...that is, what is the relationship with y and 'S(x)' after ∀?

Definitions:

∀ = forall (https://en.wikipedia.org/wiki/Turned_A)

| = such that (https://en.wikipedia.org/wiki/Set-builder_notation)

∧ = logical conjunction (and)(https://en.wikipedia.org/wiki/List_of_logic_symbols)

→ = is a function from(https://math.stackexchange.com/questions/1740154/different-arrows-in-set-theory-rightarrow-and-mapsto)

find a specific x in set S which all numbers y in S are less or equal to x.

That's super weird notation. Why not use , also there should probably a colon or dot or space after the .

E moj faksu, neka korist i od tebe

The answer is 19 because the maximum value of x for any y<=x in s is 19