You are given a code:

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

Can you predict the output of `main_solution("btamu")` 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": "btamu"}, "ref_output": "q_y_os-u-w-v-f", "ref_code": "def main_solution(x):\n    return (func_13('qyo', '_') + func_13('suwvf', '-'))", "funcname": "main_solution"}
rule