The function f(x) takes a string input and replaces every letter in the string with the letter that comes after it in the alphabet, wrapping around to the beginning of the alphabet when necessary. For example, if the input is "Rhine", the output would be "UAE", since "R" is replaced by "S", "h" is replaced by "I", "i" is replaced by "J", "n" is replaced by "O", and "e" is replaced by "P".

