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 | Venue | Attendance |
| --- | --- | --- | --- | --- | --- |
| 1.0 | September 29, 1957 | Chicago Bears | W 21-17 | City Stadium | 32132.0 |
| 2.0 | October 6, 1957 | Detroit Lions | L 24-14 | City Stadium | 32120.0 |
| 3.0 | October 13, 1957 | Baltimore Colts | L 45-17 | Milwaukee County Stadium | 26322.0 |
| 4.0 | October 20, 1957 | San Francisco 49ers | L 24-14 | Milwaukee County Stadium | 18919.0 |
| 5.0 | October 27, 1957 | at Baltimore Colts | W 24-21 | Memorial Stadium | 48510.0 |
| 6.0 | November 3, 1957 | New York Giants | L 31-17 | City Stadium | 32070.0 |
| 7.0 | November 10, 1957 | at Chicago Bears | L 21-14 | Wrigley Field | 47153.0 |
| 8.0 | November 17, 1957 | Los Angeles Rams | L 31-27 | Milwaukee County Stadium | 19540.0 |
| 9.0 | November 24, 1957 | at Pittsburgh Steelers | W 27-10 | Forbes Field | 29701.0 |
| 10.0 | November 28, 1957 | at Detroit Lions | L 18-6 | Briggs Stadium | 54301.0 |
| 11.0 | December 8, 1957 | at Los Angeles Rams | L 42-17 | Los Angeles Memorial Coliseum | 70572.0 |
| 12.0 | December 15, 1957 | at San Francisco 49ers | L 27-20 | Kezar Stadium | 59100.0 |
Question:
Opponent of at san francisco 49ers had what lowest week?
Answer:
12.0