You are given a code:

def main_solution(x):
    return ('fbhwpo' + 'kolkd')

Can you predict the output of `main_solution("ptrvf")` 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": "ptrvf"}, "ref_output": "fbhwpokolkd", "ref_code": "def main_solution(x):\n    return ('fbhwpo' + 'kolkd')", "funcname": "main_solution"}
rule