def get_position_from_periods(iteration, cumulative_period):
    """Get the position from a period list.

    It will return the index of the right-closest number in the period list.
    For example, the cumulative_period = [100, 200, 300, 400],
    if iteration == 50, return 0;
    if iteration == 210, return 2;
    if iteration == 300, return 2.

    Args:
        iteration (int): Current iteration.
        cumulative_period (list[int]): Cumulative period list.

    Returns:
        int: The position of the right-closest number in the period list.
    """
    for i, period in enumerate(cumulative_period):
        if iteration <= period:
            return i