You are given a code:

def main_solution(x):
    return func_20(func_15('ptpagq'), func_20(x, 'didb'))

Can you predict the output of `main_solution("fpk")` without writing any code? Please reason and put your final answer in the following json format: {"output": <your output>}, where <your output> should be the final string.
user
{"ref_input": {"x": "fpk"}, "ref_output": "\u00abfpd\u00bbp\u00abitk\u00bbd\u00abbp\u00bb\u00aba\u00bb\u00abg\u00bb\u00abq\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_15('ptpagq'), func_20(x, 'didb'))", "funcname": "main_solution"}
rule