You are given a code:

def main_solution(x):
    return func_13(func_20(x, 'ehnntr'), '_')

Can you predict the output of `main_solution("mvwgjjnlxm")` 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": "mvwgjjnlxm"}, "ref_output": "m_e_v_h_w_n_g_n_j_t_j_r_n_l_x_m", "ref_code": "def main_solution(x):\n    return func_13(func_20(x, 'ehnntr'), '_')", "funcname": "main_solution"}
rule