You are given a code:

def main_solution(x):
    return func_5(func_13('ngdksp', '_'), 'bg')

Can you predict the output of `main_solution("usnbvqazf")` 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": "usnbvqazf"}, "ref_output": "bgn_g_d_k_s_p", "ref_code": "def main_solution(x):\n    return func_5(func_13('ngdksp', '_'), 'bg')", "funcname": "main_solution"}
rule