You are given a code:

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

Can you predict the output of `main_solution("bmrspjbb")` 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": "bmrspjbb"}, "ref_output": "r_e_j_g_d_qb_m_r_s_p_j_b_b", "ref_code": "def main_solution(x):\n    return (func_13('rejgdq', '_') + func_13(x, '_'))", "funcname": "main_solution"}
rule