input: Write a python function to find the length of the longest word in a string.
  assert length_longest_word("The quick brown fox jumps over the lazy dog") == 5
  assert length_longest_word("A journey of a thousand miles begins with a single step") == 8
  assert length_longest_word("To be or not to be that is the question") == 8
output: def length_longest_word(s):
      words = s.split()
      longest_length = max(len(word) for word in words)
      return longest_length