You are given a code:

def main_solution(x):
    return ('vreqn' + 'ptjbl')

Can you predict the output of `main_solution("upranwrdvb")` 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": "upranwrdvb"}, "ref_output": "vreqnptjbl", "ref_code": "def main_solution(x):\n    return ('vreqn' + 'ptjbl')", "funcname": "main_solution"}
rule