You are given a code:

def main_solution(x):
    return (func_15('vms') + func_13(x, '_'))

Can you predict the output of `main_solution("twtfww")` 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": "twtfww"}, "ref_output": "\u00abv\u00bb\u00abm\u00bb\u00abs\u00bbt_w_t_f_w_w", "ref_code": "def main_solution(x):\n    return (func_15('vms') + func_13(x, '_'))", "funcname": "main_solution"}
rule