PHB p.84 tells us that
You prepare the list of paladin spells that are available for you to cast, choosing from the paladin spell list. When you do so, choose a number of paladin spells equal to your Charisma modifier + half your paladin level, rounded down (minimum of one spell).
This is somewhat ambiguous: it’s not clear whether the number is
floor( (CHA + PL) / 2 )
—as seems to be implied by the usage of a comma— or
floor( CHA + (PL/2) )
—which would make Charisma investment much more worthwhile.
Which is it? Does a 2nd-level paladin with a 16 Charisma get 2 prepared spells (first formula) or 4 (second)?