instruction:
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.
question:
['7997', 'm']
answer:
m


question:
['8975', '7199']
answer:
-1


question:
['3413', '1197', 'n', 'x', '2711', '6595', 'l', 'k', '9361', '2391', 'y', '3135', 'v', 'b', 'a', '2267', 'o', '5699', '5539', '8533', '9605', '2781']
answer:

a, b, k, l, n, o, v, x, y


