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: ['i', 'y', '8339', 'd', 'b', '7471', '6577', '9037', '4503', '6287', '1439', '8863', '9201', '2661', 'x', 'l', 'v', 'w', 'a', 'f', '8885', '519', '7631', 'g', '7203', '8605', '2429', '9165']

SOLUTION: a, b, d, f, g, i, l, v, w, x, y

PROBLEM: ['e', 'n', 'y', 'f', 'l', 'h', '455', 'y', '591', 'm', '9041', 'b', 'b', 'o', '4215', '5009', 'o', 'a', '4369', 'u', '6911', '4825', 't', 'k', '6063', '2939']

SOLUTION: a, b, e, f, h, k, l, m, n, o, t, u, y

PROBLEM: ['977', 'a', '1361', 'a', '1161', 'n', '515', 'u', '8923', 'c', '4037', '7891', '8721', 'k', 'x']

SOLUTION:
a, c, k, n, u, x