from typing import Sequence


def layers(string: str) -> Sequence[int]:
    """
    Parse hidden layer notation.

    >>> layers('2000')
    (2000,)
    >>> layers('300,300,300')
    (300, 300, 300)
    """
    result = tuple(int(layer) for layer in string.split(','))
    assert len(result) >= 1, "Must define at least one hidden layer!"
    return result