You are given a code:

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

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