You are given a code:

def main_solution(x):
    return (func_9('fpu') + func_13(x, '|'))

Can you predict the output of `main_solution("zxtnxnlo")` 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": "zxtnxnlo"}, "ref_output": "fpuupfz|x|t|n|x|n|l|o", "ref_code": "def main_solution(x):\n    return (func_9('fpu') + func_13(x, '|'))", "funcname": "main_solution"}
rule