Suppose you have collected a dataset of tweets. Each tweet in the dataset starts with a username, for example, @elonmusk. They may contain references to other users that also start with the @ character. As it is very important to keep the collected data anonymous before working with it, your task is to replace usernames at the start of the string with the special <AUTHOR> tag and all other handles with <HANDLE>.
You will get a tweet as input, print out the modified version of it.
