python – Making string modifying code more efficient

I have been practicing Python Practice questions and came across this question:

Write a Python program to add ‘ing’ at the end of a given string
(length should be at least 3).

If the given string already ends with ‘ing’ then add ‘ly’ instead.

If the string length of the given string is less than 3, leave it
unchanged. Sample String : ‘abc’

Expected Result : ‘abcing’

Sample String : ‘string’

Expected Result : ‘stringly’

Here’s my code:

string = input()
if len(string) < 3:
  print(string)
elif string(-3:) == 'ing':
  print(string + 'ly')
else:
  print(string + 'ing')

However something about this code seems wrong though it works fine I feel it smells bad, I can’t pinpoint why