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:
| Pos | No | Driver | Constructor | Laps | Time/Retired | Grid | Points |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | 4 | Robert Kubica | BMW Sauber | 70 | 1:36:24.227 | 2 | 10 |
| 2 | 3 | Nick Heidfeld | BMW Sauber | 70 | +16.495 | 8 | 8 |
| 3 | 9 | David Coulthard | Red Bull-Renault | 70 | +23.352 | 13 | 6 |
| 4 | 12 | Timo Glock | Toyota | 70 | +42.627 | 11 | 5 |
| 5 | 2 | Felipe Massa | Ferrari | 70 | +43.934 | 6 | 4 |
| 6 | 11 | Jarno Trulli | Toyota | 70 | +47.775 | 14 | 3 |
| 7 | 17 | Rubens Barrichello | Honda | 70 | +53.597 | 9 | 2 |
| 8 | 15 | Sebastian Vettel | Toro Rosso-Ferrari | 70 | +54.120 | 19 | 1 |
| 9 | 23 | Heikki Kovalainen | McLaren-Mercedes | 70 | +54.433 | 7 |  |
| 10 | 7 | Nico Rosberg | Williams-Toyota | 70 | +54.749 | 5 |  |
| 11 | 16 | Jenson Button | Honda | 70 | +1:07.540 | 20 |  |
| 12 | 10 | Mark Webber | Red Bull-Renault | 70 | +1:11.299 | 10 |  |
| 13 | 14 | Sébastien Bourdais | Toro Rosso-Ferrari | 69 | +1 Lap | 18 |  |
| Ret | 21 | Giancarlo Fisichella | Force India-Ferrari | 51 | Spun off | 17 |  |
| Ret | 8 | Kazuki Nakajima | Williams-Toyota | 46 | Accident | 12 |  |
| Ret | 5 | Fernando Alonso | Renault | 44 | Spun off | 4 |  |
| Ret | 6 | Nelson Piquet Jr. | Renault | 43 | Brakes | 15 |  |
| Ret | 1 | Kimi Räikkönen | Ferrari | 19 | Collision | 3 |  |
| Ret | 22 | Lewis Hamilton | McLaren-Mercedes | 19 | Collision | 1 |  |
| Ret | 20 | Adrian Sutil | Force India-Ferrari | 13 | Gearbox | 16 |  |
Question:
how many cars spun off the track?
Answer:
2