def check_seat(y, x, lst):
    """
    Check seat value in a given list.

    Args:
        y: The column index of the seat.
        x: The row index of the seat.
        list: The list the seat is in.

    Returns:
        The value of the seat.
    """
    if y < 0 or x < 0:
        return None
    else:
        try:
            return lst[y][x]
        except IndexError:
            return None