input: Write a python function to count the number of words in a string.
  assert count_words("There are 5 words in the given string.") == 7
  assert count_words("To count the number of words in a string, you can use the len() or count() functions in Python.") == 20
  assert count_words("num_words = len(string.split())") == 4
output: def count_words(s):
      return len(s.split())