You are given a code:

def main_solution(x):
    return func_13(func_20(x, 'wkfubn'), '-')

Can you predict the output of `main_solution("zunsvzcttb")` 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": "zunsvzcttb"}, "ref_output": "z-w-u-k-n-f-s-u-v-b-z-n-c-t-t-b", "ref_code": "def main_solution(x):\n    return func_13(func_20(x, 'wkfubn'), '-')", "funcname": "main_solution"}
rule