Some would say the it improper in English to end a sentence with a preposition (at) but that is not so much the case anymore.
Wasn't that one of Noah Webster's hobby horses that got perpetuated for no other reason than that he said so.
I think it was first put forward seriously in Lowth's A Short Introduction to English Grammar of 1755, the first prescriptivist grammar, and and then it was perpetuated by 19th century prescriptivists.
Whatever Noah Webster might have thought about it. it is not an idea shared by his successors at Merriam-Webster.