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: ['u', '4731', 'l', 'p', '1997', '601', 'n', 'l', 'p', '211', '7355', '6537', 'w', 'x', '1741', '8145', '3689', 'm', 'y', '6945']

SOLUTION: l, m, n, p, u, w, x, y

PROBLEM: ['l', '6313', '3199', 'w', '249', '8747', '7391', '3871', '173', 'x', 'o', '8647', '4413', '3645', '6123', '701', 'q', '2147', '4289', '7333', '533']

SOLUTION: l, o, q, w, x

PROBLEM: ['1439', '3049', '9849', 'e', 'i', '7523', 'f', 'd', '6929', 'p', 'q', 'e', '6279', '2721', '7393', '1399', 's', '2927', 'g', '9227', 'z', '803', '6015', 'r', 'c', 'u']

SOLUTION:
c, d, e, f, g, i, p, q, r, s, u, z