Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| Week | Date | Opponent | Result | Attendance |
| --- | --- | --- | --- | --- |
| 1.0 | September 30, 1956 | at San Francisco 49ers | W 38–21 | 41751.0 |
| 2.0 | October 7, 1956 | at Chicago Cardinals | L 35–27 | 21799.0 |
| 3.0 | October 14, 1956 | at Cleveland Browns | W 21–9 | 60042.0 |
| 4.0 | October 21, 1956 | Pittsburgh Steelers | W 38–10 | 48108.0 |
| 5.0 | October 28, 1956 | Philadelphia Eagles | W 20–3 | 40960.0 |
| 6.0 | November 4, 1956 | at Pittsburgh Steelers | W 17–14 | 31240.0 |
| 7.0 | November 11, 1956 | Chicago Cardinals | W 23–10 | 62410.0 |
| 8.0 | November 18, 1956 | at Washington Redskins | L 33–7 | 26261.0 |
| 9.0 | November 25, 1956 | Chicago Bears | T 17–17 | 55191.0 |
| 10.0 | December 2, 1956 | Washington Redskins | W 28–14 | 26261.0 |
| 11.0 | December 9, 1956 | Cleveland Browns | L 24–7 | 27707.0 |
| 12.0 | December 15, 1956 | at Philadelphia Eagles | W 21–7 | 16562.0 |
Question:
What's the highest week for the day of October 21, 1956?
Answer:
4.0