You are given a code:

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

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