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: ['y', 'g', '107', '4899', '6357', '9777', 'k', '1865', '7029', 'q', 'x', '7051', 's', '6125', '4285', '2731', 'z', 'a', '737', '6137']

SOLUTION: a, g, k, q, s, x, y, z

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: ['7501', 'x', 'c', 'a', 'z', 'u', '589', '3541', 'c', 't', '6547', '8067', '5687', '5639', 'g', '8007', 'f', '6859', '6883', 'i', 'l', '2195', '3543', '5959', 'j', '4891', '6683', 'r', 'e', '7973', '9547', '285', '5969', 'm', '9153', '3079']

SOLUTION:
a, c, e, f, g, i, j, l, m, r, t, u, x, z