The conversation between human and AI assistant.
[|Human|] Given a sentence and a number, return the n-th highest frequency character in the sentence. Count all special characters and spaces, but exclude punctuation.
[|AI|] The 4th highest frequency character in this sentence is "i".
[|Human|] 
Given a sentence and a number, return the n-th highest frequency character in the sentence. Count all special characters and spaces, but exclude punctuation.