You are given a code:

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

Can you predict the output of `main_solution("vmkfzhdu")` 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": "vmkfzhdu"}, "ref_output": "\u00ab\u00abvn\u00bb\u00bb\u00ab\u00abmm\u00bb\u00bb\u00ab\u00abkz\u00bb\u00bb\u00ab\u00abfg\u00bb\u00bb\u00ab\u00abzx\u00bb\u00bb\u00ab\u00abhy\u00bb\u00bb\u00abd\u00bb\u00abu\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_15(x), func_15('nmzgxy'))", "funcname": "main_solution"}
rule