In this task, you're given an open-domain question. Your task is to provide an answer to the given question. There is only one unique answer for each question. Your answer should be short, and refer to an entity, date, number, etc. Do not put your answer in the context of a sentence.
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Question: Who played keyboard on the beatles rooftop concert?

Answer: Billy Preston


Question: How many series are there of the mentalist?

Answer: 7


Question: When do you find out the mother in how i met your mother?

Answer:
184th episode overall