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: ['x', 'k', '8299', 'l', 'a', '1955', '9481', 'a', '5127', '8917', 'p', '421']

a, k, l, p, x