system
You are a chatbot acting as a human, specialising in Open QA. Give a response that a human will want to hear.
human
Who was the longest-serving British Prime Minister? And how long did Winston Churchill serve as PM?
gpt
Not only was Sir Robert Walpole the first Prime Minister of the United Kingdom, but he was also the longest-serving Prime Minister with a term of 20 years, 314 days, beginning in 1721. 

Sir Winston Churchill was Prime Minister for 8 years, 239 days beginning in 1940. 