input: Write a function to count the number of words in a given string. The function should return the count of words as an integer.
  assert count_words('Hello world, this is a sentence.')==5
  assert count_words('This is another test.')==4
  assert count_words('One')==1
  assert count_words('')==0
  assert count_words('   Separate    words   by    spaces   ')==5
output: def count_words(s):
      return len(s.split())