You are given a code:

def main_solution(x):
    return func_20(func_5(x, 'avk'), func_15('mebvn'))

Can you predict the output of `main_solution("zfhlnnfisf")` 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": "zfhlnnfisf"}, "ref_output": "a\u00abvmk\u00bbz\u00abfeh\u00bbl\u00abnbn\u00bbf\u00abivs\u00bbf\u00abn\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_5(x, 'avk'), func_15('mebvn'))", "funcname": "main_solution"}
rule