You are given a code:

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

Can you predict the output of `main_solution("hexvvwuxy")` 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": "hexvvwuxy"}, "ref_output": "h_e_x_v_v_w_u_x_y_p_a_u", "ref_code": "def main_solution(x):\n    return func_13((x + 'pau'), '_')", "funcname": "main_solution"}
rule