You are given a code:

def main_solution(x):
    return func_20(func_13(x, '_'), func_15('kpgrvo'))

Can you predict the output of `main_solution("smbnhb")` 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": "smbnhb"}, "ref_output": "s\u00ab_km\u00bb_\u00abbp_\u00bbn\u00ab_gh\u00bb_\u00abbr\u00bb\u00abv\u00bb\u00abo\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_13(x, '_'), func_15('kpgrvo'))", "funcname": "main_solution"}
rule