def get_preresolution(file: str) -> int:
    """
    Read pre file and returns number of unknowns

    :param file: pre file
    :return: number of unknowns
    """
    with open(file) as f:
        content = f.readlines()
    ind = [idx for idx, s in enumerate(content) if '$DofData' in s][0]
    tmp = content[ind + 5].split()[-1]

    return int(tmp)