You are given a code:

def main_solution(x):
    return func_13(func_20('mbprvv', x), '_')

Can you predict the output of `main_solution("fzzbhdh")` 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": "fzzbhdh"}, "ref_output": "m_f_b_z_p_z_r_b_v_h_v_d_h", "ref_code": "def main_solution(x):\n    return func_13(func_20('mbprvv', x), '_')", "funcname": "main_solution"}
rule