input: Write a python function to capitalize words with more than 3 characters in a string.
  assert capitalize_more_than_3_characters("this is a test string") == "This is a Test String"
  assert capitalize_more_than_3_characters("hello world") == "Hello World"
  assert capitalize_more_than_3_characters("a big blue sky") == "a Big Blue Sky"
output: def capitalize_more_than_3_characters(s):
      return ' '.join([word.capitalize() if len(word) > 3 else word for word in s.split()])