You are given a code:

def main_solution(x):
    return (func_15('mfrh') + func_13(x, '_'))

Can you predict the output of `main_solution("iooikwfca")` 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": "iooikwfca"}, "ref_output": "\u00abm\u00bb\u00abf\u00bb\u00abr\u00bb\u00abh\u00bbi_o_o_i_k_w_f_c_a", "ref_code": "def main_solution(x):\n    return (func_15('mfrh') + func_13(x, '_'))", "funcname": "main_solution"}
rule