You are given a code:

def main_solution(x):
    return (func_13(x, '_') + func_17('tlrx'))

Can you predict the output of `main_solution("fsivrwzu")` 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": "fsivrwzu"}, "ref_output": "f_s_i_v_r_w_z_uxrlt", "ref_code": "def main_solution(x):\n    return (func_13(x, '_') + func_17('tlrx'))", "funcname": "main_solution"}
rule