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: ['459', '1729', 'b', 'c', '9619', '4461', '4347', '6733', 'i', '3631', 's', 'j', 'i', 'r', '5293', 'q', '7397', '4309', 'c', 'n', 'k', '197', 'q', '8139']

SOLUTION: b, c, i, j, k, n, q, r, s

PROBLEM: ['9273', '5219', 'e', '9413', 'v', 'h', '5657', '797', '2303', '2119', '4791', '2757', '4983', 'h', '9681', '4503', '6657', 't', 'i', 'g', '9375', '9901', 'm', 'y', '6461', 'h', '6663', '9493', '5897', '8829', 'd', 'x', '901', '833', 'u']

SOLUTION: d, e, g, h, i, m, t, u, v, x, y

PROBLEM: ['l', '707', '6987', '3815', '3777', '6963', 'x', 'u', 'z', 'y', 'c', 'p', 'f', 't', 'n', '2787', 'o', 'c', '5033', 'f', '2743', '5029', 'r', '8901']

SOLUTION:
c, f, l, n, o, p, r, t, u, x, y, z