You are given a code:

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

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