You are given a code:

def main_solution(x):
    return (func_4('bpd') + func_13(x, '_'))

Can you predict the output of `main_solution("kdtsvpjqxz")` 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": "kdtsvpjqxz"}, "ref_output": "bpdk_d_t_s_v_p_j_q_x_z", "ref_code": "def main_solution(x):\n    return (func_4('bpd') + func_13(x, '_'))", "funcname": "main_solution"}
rule