You are given a code:

def main_solution(x):
    return func_13(func_1('ihzftk', 4), '_')

Can you predict the output of `main_solution("bgkk")` 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": "bgkk"}, "ref_output": "i_h_z_f_t_k_i_h_z_f_t_k_i_h_z_f_t_k_i_h_z_f_t_k", "ref_code": "def main_solution(x):\n    return func_13(func_1('ihzftk', 4), '_')", "funcname": "main_solution"}
rule