import os
from io import StringIO


def readfile(path: str) -> str:
    srcio = StringIO()
    with open(path + '.bu4') as file:
        for line in file:
            if line.startswith('@'):
                srcio.write(readfile(os.path.join(path, '..', line.removeprefix('@').strip())))
            else:
                srcio.write(line)
    return srcio.getvalue()