def get_model_top_scope_name(model_name, problem_name):
    """ Returns the top scope name of all models.

    Args:
        model_name: The model string.
        problem_name: The problem name.

    Returns: A str.
    """
    if model_name is None:
        model_name = "SequenceToSequence"
    return problem_name or model_name.split(".")[-1]