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: ['c', '7039', 'g', '1899', 'r', '507', 'c', '2587', '3865', '1729', '3927', 'r', '3535', '2791', 'm', 'l', 'r']

SOLUTION: c, g, l, m, r

PROBLEM: ['f', '6817', 'f', 'd', '3835', '3051', 'u', 'l', '7679', 'b', '3931', '1441', 'q', '8675', 's', '5487', 'y', '2279', 'x', 'y', '9513', '2875', '1771', '879', '2927', '3469', 'v', 't', 'k', '9991', '2565', '7345', '973', 'w', 'i', '6105']

SOLUTION: b, d, f, i, k, l, q, s, t, u, v, w, x, y

PROBLEM: ['o', '2515', '1537', 't', 'h', '6577', 't', '9523', 'o', '4399', '8835', 'o', 'a', '3609', 'y', '5065', '4599', 'r', '7549', '2121', '4719', '6131', 'l', 'e', '6155', '2193', 'w', '5595', 's', 'j', '5755', '8341', 'h', 'g', 't', '4783', '6551', 'u', '5875']

SOLUTION:
a, e, g, h, j, l, o, r, s, t, u, w, y