input: Write a function to count the number of words with exactly 5 letters in a given string.
  assert count_words_length("The quick brown fox jumped over the lazy dog.") == 1
  assert count_words_length("Apple is a fruit and there are many apples.") == 2
  assert count_words_length("Five letter words are not that common.") == 2
output: def count_words_length(s: str) -> int:
      words = s.split()
      return sum(1 for word in words if len(word) == 5)