You are given a code:

def main_solution(x):
    return func_20(('qhcdxr' + 'yvjr'), func_13(x, '_'))

Can you predict the output of `main_solution("ckavzjtbmf")` 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": "ckavzjtbmf"}, "ref_output": "qch_ckd_xar_yvv_jzr_j_t_b_m_f", "ref_code": "def main_solution(x):\n    return func_20(('qhcdxr' + 'yvjr'), func_13(x, '_'))", "funcname": "main_solution"}
rule