You are given a code:

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

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