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.

['3797', '6117', 'x']
x
Given the list ['3797', '6117', 'x'], there is only one alphabet, 'x'. Therefore, the resulting string will be "x"..