You are given a code:

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

Can you predict the output of `main_solution("bkzekkffqg")` 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": "bkzekkffqg"}, "ref_output": "g_y_h_m_h_p_d_y_u_d", "ref_code": "def main_solution(x):\n    return func_13(('gyhmhp' + 'dyud'), '_')", "funcname": "main_solution"}
rule