TASK 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.
PROBLEM: ['w', '6291', '3939', '9569', 'u', '1635', '3359', '8335', 'n', '2799', '7359', 'k', 'm', '2817']

SOLUTION: k, m, n, u, w

PROBLEM: ['7777', '6223', 'k', 'k', 'd', '9743', '189', '7705', 'c', '6115', '4275']

SOLUTION: c, d, k

PROBLEM: ['a', '4353', '7469', '1423', 'h', '9391', '7119', '2793', '7591', '2517', '7579', '1139', '6631', '5043', '3627', '5543', '729', '1191', 'k']

SOLUTION:
a, h, k