You are given a code:

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

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