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: ['749', 'r', 'a', 's', 't', '5905', 'm', 'd', '8437', '4583']

SOLUTION: a, d, m, r, s, t

PROBLEM: ['1595', '2915', 'o', 't', 'c', 'h', '3969', '5407']

SOLUTION: c, h, o, t

PROBLEM: ['r', 's', 'm', '8939', '6357', 'g', 'x', '3251', '6801', 'c', 'k', 'a', '9413', 'v', 'p', 'c', 's', 'w', '3737', '5777', 'q', 'm', 'a', '697', '8929', '9227', '515']

SOLUTION:
a, c, g, k, m, p, q, r, s, v, w, x