You are given a code:

def main_solution(x):
    return func_4('ymbu')

Can you predict the output of `main_solution("mjobeix")` 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": "mjobeix"}, "ref_output": "ymbu", "ref_code": "def main_solution(x):\n    return func_4('ymbu')", "funcname": "main_solution"}
rule