This is the 570th most frequent Serbian word.
њен
"Њен" means "her" or "hers" in English.
Here, 'њена' is the feminine form of the possessive pronoun 'her', matching the noun 'оловка' (pencil), which is feminine in Serbian.
Ово је њена оловка.
This is her pencil.
In this sentence, 'њена' indicates possession and is used without the noun, implying 'book' which is feminine (non-neutral).
Књига је њена.
The book is hers.
Here, 'њеном' is the locative case form of the possessive pronoun 'her', agreeing in gender, number, and case with 'успеху' (success).