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', 'n', '729', '2491', 'n', 'x', '915', '1869', 'z', '8491', '9947', '561', '829', 'n', 't', 'i']

SOLUTION: i, n, t, w, x, z

PROBLEM: ['h', 'g', 'j', 'i', 'y', '7799', 'y', 'e', 'y', 'e', '6757', '3349', '1213', '191', 'd', '2149', '849', '8325', 'b', '6087', 'w', '7211', '7801']

SOLUTION: b, d, e, g, h, i, j, w, y

PROBLEM: ['5011', 'l', '7511', 'b', 'v', '2877', 'f', 'n', 'c', '4647', '709', '7615', 'f', '6953', '3607', '4883', '5073', 'd', '9717', 'j', 'l', 'o', 'l', '8719', '5475', '5803', 'a', '1001']

SOLUTION:
a, b, c, d, f, j, l, n, o, v