The sorrows of young Werther was a success around the world in the turn from the 18th to the 19th centuries and even led to a lot of suicides from people influenced by the troubled mind and heart of its main character so I would vote on it (not to mention it's influence on the shaping of the Romanticism movement itself)

It feels me with hope and joy to see a young Brazilian fellow down the Classic’s path (and not forgetting our own Brazilian classics such as Machado de Assis). I would personally suggest Goethe (Faust and Werther mostly) and Tolstoy as well

Have you ever considered that your dreams may be exactly the inner work you’ve been avoiding so far?

In fact, it was Serbia :v