You are given a code:

def main_solution(x):
    return func_13(func_5('mgkla', 'ybpb'), '_')

Can you predict the output of `main_solution("jmrbcfgi")` 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": "jmrbcfgi"}, "ref_output": "y_b_p_b_m_g_k_l_a", "ref_code": "def main_solution(x):\n    return func_13(func_5('mgkla', 'ybpb'), '_')", "funcname": "main_solution"}
rule