Unfortunately, viewers are giving the drama bad ratings because of the type of story it contains.
But this doesn't make sense, because from the description you can think that it'll contain something in that regard.

This is a beautiful story come to life by great acting. This is a Student/Teacher story, BUT NOT inappropriate at all in our eyes. We interpreted it as them having mutual respect for each other and love for math whilst in school. Please do give it a try, BUT only if you're comfortable with this type of relationship. We're not going to give spoilers. We will however say that this was a hidden gem we're glad we discovered.