You are given a code:

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

Can you predict the output of `main_solution("afzbftmkym")` 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": "afzbftmkym"}, "ref_output": "a_f_z_b_f_t_m_k_y_m_b_k_u_j_d_s", "ref_code": "def main_solution(x):\n    return func_13((x + 'bkujds'), '_')", "funcname": "main_solution"}
rule