You are given a code:

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

Can you predict the output of `main_solution("cnvgblnoff")` 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": "cnvgblnoff"}, "ref_output": "wlbc_n_v_g_b_l_n_o_f_f", "ref_code": "def main_solution(x):\n    return func_5(func_13(x, '_'), 'wlb')", "funcname": "main_solution"}
rule