[PeterT]

try

program:
words=raw_field('#words');
shelf_name=cmp(words, 1000, 'Short Story', 'Novel', 'Novel');
shelf_name=cmp(words, 5000, shelf_name, 'Medium', 'Medium');
shelf_name=cmp(words, 20000, shelf_name, 'Long', 'Long');
shelf_name=cmp(words, 50000, shelf_name, 'Epic', 'Epic');

The idea is
If the words are < 1000 then use Short Story else Novel
If the words are < 5000 then use the already set name (either Short Story or Novel) else use Medium
If the words are < 20000 then use the already set name (either Short Story, Novel or Medium) else use Long
If the words are < 50000 then use the already set name (either Short Story, Novel, Medium or Long) else use Epic