You are given a code:

def main_solution(x):
    return ('fsf' + 'avy')

Can you predict the output of `main_solution("cqtb")` 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": "cqtb"}, "ref_output": "fsfavy", "ref_code": "def main_solution(x):\n    return ('fsf' + 'avy')", "funcname": "main_solution"}
rule