Could you please give your opinion?
4 is not a bad number. Number 4 is a number that has a strong grounding energy, it will teach one the lessons he or she needs to learn in order to move forward in life. We have 4 seasons, 4 directions, we do not consider them inauspicious, do we?
Unless you use Cantonese on a daily basis, I would suggest not to worry about it. You can also encircle the number in color red, it is a feng shui cure.
I lived in a place that had two 4s for a while and I've learned some of the most important life lessons there. Very grounding and strong energy. It will "ground" you till you are done with the lesson, whatever this life lesson this might be.
However, what would worry me in your case is the luck of the previous occupants and the energy they are leaving in the space. You would have to do some strong energy clearing (feng shui space clearing and smudging, etc) if you want to move into that apartment.