The function f(x) performs the following operations on the input string:
1. If the input string contains only alphabetic characters, each character is replaced with the next character in the alphabetical order (wrapping around from 'z' to 'a').
2. If the input string contains only numeric characters, it remains unchanged.
3. If the input string contains a combination of alphabetic and numeric characters, each alphabetic character is replaced with the next character in the alphabetical order, and the numeric characters remain unchanged.

