def get_min_samples(N):
    """Get the `min_samples` attribute based on the number of
    users who have transcribed the subject.  These values were
    found based on example data from ASM.

    Parameters
    ----------
    N : integer
        The number of users who have see the subject

    Returns
    -------
    min_samples : integer
        The value to use for the min_samples keyword in OPTICS
    """
    if N <= 6:
        return 2
    elif N <= 10:
        return 3
    elif N <= 15:
        return 4
    elif N <= 20:
        return 5
    else:
        return int(0.25 * N)
