You are given a code:

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

Can you predict the output of `main_solution("cvae")` 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": "cvae"}, "ref_output": "m_s_n_d_b_f_i_w_t_e_a", "ref_code": "def main_solution(x):\n    return func_13(('msndbf' + 'iwtea'), '_')", "funcname": "main_solution"}
rule