The first answer mistakenly translates "elemento" as "element", whereas in truth it is usually correctly translated as "factor". I speculatively added the alternative term "argument", although to be certain I would have to know the context. "To add" may be the most frequent translation of the Spanish "sumar"; however "add" is a very general term: you add ingredients to a recipe, you add details to a description, etc. "To contribute" on the other hand is more specific. Accordingly the meaning intended is clear, unlike the result when you use "to add".