This is the 527th most frequent Serbian word.
првих
"Првих" means "the first" (genitive plural form).
Here, 'првих' is used as an ordinal adjective in the genitive plural to describe "странa" (pages), meaning the first set of items in a sequence.
Завршио сам првих десет страна у књизи.
I finished the first ten pages of the book.
In this sentence, 'првих' is employed to indicate the initial days in a temporal sequence, modifying "дана" in genitive plural form.
Првих неколико дана на новом послу били су изазовни.
The first few days at the new job were challenging.
'Првих' here modifies the noun phrase "годину дана" in the genitive singular form to express the importance of the initial period.