Here's the completed code:
```
# Import defaultdict
from collections import defaultdict
# Save the fifth document: doc
doc = corpus[4]
# Sort the doc for frequency: bow_doc
bow_doc = sorted(doc, key=lambda w: w[1], reverse=True)
# Print the top 5 words of the document alongside the count
for word_id, word_count in bow_doc[:5]:
print(dictionary.get(word_id), word_count)
# Create the defaultdict: total_word_count
total_word_count = defaultdict(int)
# Iterate over each word ID and count in each document
for word_id, word_count in itertools.chain.from_iterable(corpus):
# Increment the count of the word ID
total_word_count[word_id] += word_count
```
The code uses `sorted()` to sort `doc` by frequency and assigns it to `bow_doc`. It then prints the