You are given a code:

def main_solution(x):
    return (func_13('rpu', '_') + func_13('lxilk', '_'))

Can you predict the output of `main_solution("kpaenjfd")` 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": "kpaenjfd"}, "ref_output": "r_p_ul_x_i_l_k", "ref_code": "def main_solution(x):\n    return (func_13('rpu', '_') + func_13('lxilk', '_'))", "funcname": "main_solution"}
rule