You are given a code:

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

Can you predict the output of `main_solution("png")` 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": "png"}, "ref_output": "\u00abK\u00bb\u00abZ\u00bb\u00abW\u00bb\u00abX\u00bb\u00abL\u00bb", "ref_code": "def main_solution(x):\n    return func_15(('kzwxl').upper())", "funcname": "main_solution"}
rule