Definition: In this task, you are given an input list A comprising of numbers and alphabets. You need to extract and sort the unique alphabets in the list. The alphabets in the input list will only be in lowercase. Return -1 if there is no alphabet in the input list.
Input: ['b', '9785', '7883', '2435', '5829', '1493', 'w', 'g', '7375']

b, g, w