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: ['e', '779', '9705', 'v', 't', 'l', 'y', '9455', 'e', 'i', '6799']

e, i, l, t, v, y