The function f(x) takes a string input and returns a string output. The output appears to be a modified version of the input string, with some characters replaced by other characters. The specific modifications made to the input string seem to depend on the length of the string. For example, for inputs with a length of 5, the first and last characters are swapped, while for inputs with a length of 10, the first and last characters are replaced by the characters "A" and "Z", respectively.

