Based on the given tweet, determine the level of sadness the author is experiencing. Choose from the following options: 0: no sadness can be inferred, 1: low amount of sadness can be inferred, 2: moderate amount of sadness can be inferred, 3: high amount of sadness can be inferred.
Tweet: Incredibly shocked and disappointed with @united customer service. Really making me rethink flying with them in the future. #unhappy
3: high amount of sadness can be inferred