def _get_dp_bin(dp):
    """Returns lower bin width for the given depth.

    Bin width

    - 0..19: 1bp
    - 20..49: 5bp
    - 50..199: 10bp
    - 200..: = 200
    """
    if dp < 20:
        return dp
    elif dp < 50:
        return (dp // 2) * 2
    elif dp < 200:
        return (dp // 5) * 5
    else:
        return 200