def interspace(btn_h, btn_count, scr_h):
    """
    Given the height of a button, the number of buttons to be displayed, and
    the height of the curses window the buttons will be displayed within,
    returns the number of lines to be given between each button for maximum
    vertical spacing.
    """
    return (scr_h - btn_h * btn_count) // (btn_count - 1)
