Complete the function that takes one argument, a list of words, and returns the length of the longest word in the list.
For example: 
```python
['simple', 'is', 'better', 'than', 'complex'] ==> 7
```
Do not modify the input list.
def longest(words):
    return len(max(words, key=len))
def longest(words):
    return len(max(words, key=len))