You are given a code:

def main_solution(x):
    return func_20(func_15('npvq'), func_20(x, x))

Can you predict the output of `main_solution("bqtlddfud")` 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": "bqtlddfud"}, "ref_output": "\u00abbnb\u00bbq\u00abqpt\u00bbt\u00ablvl\u00bbd\u00abdqd\u00bbdffuudd", "ref_code": "def main_solution(x):\n    return func_20(func_15('npvq'), func_20(x, x))", "funcname": "main_solution"}
rule