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: ['r', '5851', 'z', '5137', '4987', 'a', 'b', 'v', '9191']

a, b, r, v, z