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: ['6955', '721', '2763', '8121', '9109', '6341', 'p', 't', 'x', '6963', '1137', 'z', 'u', '1949', '7029', 't', '9539', 'a', 'u', '1873']

SOLUTION: a, p, t, u, x, z

PROBLEM: ['4945', 'i', 'h', 's', '8925', 'i', '3995', 'f', '813', '1823', '3475', 'q', '2463', '9487', 'c', 'c', 'n', 'y', 's', '6269', 'a', 'u', 'd', 'd', '9291', '3187', '545', '7929', 'd', '1007', '7579', '8421', '4033', 'v', 'c', 'e', 'n', 'j']

SOLUTION: a, c, d, e, f, h, i, j, n, q, s, u, v, y

PROBLEM: ['5867', 't', '3201', 'i', 'm', 'a', '5287', '8637', '6557', '9709', '6959', 'n', '6687', 'h', '2079', '6883', 'z', 'v', 'k', '6351', 'b', 'l', 'a', 'i', '2663', 'd', 'x', '6245', '6601', '8733', 'y', '7669', 'y', '8551']

SOLUTION:
a, b, d, h, i, k, l, m, n, t, v, x, y, z