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: ['4925', 'i', 'q', 'k', '7615', 'r', '7217', 'o', '8097', '9151']

SOLUTION: i, k, o, q, r

PROBLEM: ['t', 'c', 'r', '4459', 'o', '1407', 'x', '1515', '331', 'm', '1535', 'p', 'u', 'g', '2513', 'o', '7827', '8149', 'd', 'z', 'q', '5655', 'x', '9997', '2809', 'g', 'h', '6309', 'a', 'j', '9773', '2115', 't', '9113', 'q', 'o', '427', 's', '3815', '5423', 's', 'n', 'i', 'o', '3643']

SOLUTION: a, c, d, g, h, i, j, m, n, o, p, q, r, s, t, u, x, z

PROBLEM: ['6515', 'n', 'k', 'l', '6295', '8519', '4879', '4273', 'i', '8735', '1817', 'u', '4271', 's', 'n', 'q', '2729', 'a', '9413', '2027']

SOLUTION:
a, i, k, l, n, q, s, u