Definition: Given a 'poster' sentence and a corresponding 'response' (often, from Facebook or Reddit)classify the sentiment of the given response into four categories: 1) Positive, 2) Negative, 3) Neutral, and 4) Mixed if it contains both positive and negative.
Input: Poster: Excited to be a part of the fifth annual Social Good Summit!  Responser: Caitlin, I'm proud of you! Keep up the good work. :-)
