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: ['7975', 'm', '1279', 'n', 'y', 'b', 'd', 'z', '871', '799', 'j']

b, d, j, m, n, y, z