You are given a code:

def main_solution(x):
    return func_20(func_4(x), func_15('tdbk'))

Can you predict the output of `main_solution("ibbwcd")` 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": "ibbwcd"}, "ref_output": "i\u00abbtb\u00bbw\u00abcdd\u00bb\u00abb\u00bb\u00abk\u00bb", "ref_code": "def main_solution(x):\n    return func_20(func_4(x), func_15('tdbk'))", "funcname": "main_solution"}
rule