You are given a code:

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

Can you predict the output of `main_solution("rtbluacmk")` 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": "rtbluacmk"}, "ref_output": "r-t-b-l-u-a-c-m-ku_u_d_k_g_o", "ref_code": "def main_solution(x):\n    return (func_13(x, '-') + func_13('uudkgo', '_'))", "funcname": "main_solution"}
rule