Create a function to extract the name of the subreddit from its URL.
SubReddit("https://www.reddit.com/r/funny/") ➞ "funny"
SubReddit("https://www.reddit.com/r/relationships/") ➞ "relationships"
SubReddit("https://www.reddit.com/r/mildlyinteresting/") ➞ "mildlyinteresting"N/A