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.
Input: ['3909', 'o', 'y', 'f', 't', 'u', 'c', '3715']

c, f, o, t, u, y