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: ['j', '425', '6223', '6631', 'y', '7649', 'r', 'a', '7933', '7947', 'l', 'l', '8755', 'g', 'b', '3351', '49', 'v', 'm', 'x', '3291', '1007', '1401', 'z', 'q', 'a']

SOLUTION: a, b, g, j, l, m, q, r, v, x, y, z

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: ['r', '373', 'f', '3801', '4079', '6897', '809', 's', '3579', 'x', '8939', 'h', '1979', 'o', 'p', '8759', '6995', '7439', '2659', 'a', 'l', 'v']

SOLUTION:
a, f, h, l, o, p, r, s, v, x