You are given a code:

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

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