You are given a code:

def main_solution(x):
    return func_20(func_15(x), func_1('nbla', 4))

Can you predict the output of `main_solution("stbnr")` 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": "stbnr"}, "ref_output": "\u00abnsb\u00bbl\u00abatn\u00bbb\u00ablba\u00bbn\u00abbnl\u00bba\u00abnrb\u00bbla", "ref_code": "def main_solution(x):\n    return func_20(func_15(x), func_1('nbla', 4))", "funcname": "main_solution"}
rule