You are given a code:

def main_solution(x):
    return (func_15('rnxphf')).upper()

Can you predict the output of `main_solution("ujpztbc")` 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": "ujpztbc"}, "ref_output": "\u00abR\u00bb\u00abN\u00bb\u00abX\u00bb\u00abP\u00bb\u00abH\u00bb\u00abF\u00bb", "ref_code": "def main_solution(x):\n    return (func_15('rnxphf')).upper()", "funcname": "main_solution"}
rule