You are given a code:

def main_solution(x):
    return func_20('ypn', 'ipbm')

Can you predict the output of `main_solution("gzkmff")` 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": "gzkmff"}, "ref_output": "yippnbm", "ref_code": "def main_solution(x):\n    return func_20('ypn', 'ipbm')", "funcname": "main_solution"}
rule