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 | 7 | Jo Bonnier | BRM | 75 | 2:05:26.8 | 1 | 8 |
| 2 | 8 | Jack Brabham | Cooper-Climax | 75 | + 14.2 | 2 | 6 |
| 3 | 9 | Masten Gregory | Cooper-Climax | 75 | + 1:23.0 | 7 | 4 |
| 4 | 12 | Innes Ireland | Lotus-Climax | 74 | + 1 Lap | 9 | 3 |
| 5 | 1 | Jean Behra | Ferrari | 74 | + 1 Lap | 4 | 2 |
| 6 | 3 | Phil Hill | Ferrari | 73 | + 2 Laps | 12 |  |
| 7 | 14 | Graham Hill | Lotus-Climax | 73 | + 2 Laps | 5 |  |
| 8 | 10 | Maurice Trintignant | Cooper-Climax | 73 | + 2 Laps | 11 |  |
| 9 | 16 | Cliff Allison | Ferrari | 71 | + 4 Laps | 15 |  |
| 10 | 15 | Carel Godin de Beaufort | Porsche | 68 | + 7 Laps | 14 |  |
| Ret | 11 | Stirling Moss | Cooper-Climax | 62 | Gearbox | 3 | 1 |
| Ret | 6 | Harry Schell | BRM | 46 | Gearbox | 6 |  |
| Ret | 2 | Tony Brooks | Ferrari | 42 | Oil Leak | 8 |  |
| Ret | 5 | Carroll Shelby | Aston Martin | 25 | Engine | 10 |  |
| Ret | 4 | Roy Salvadori | Aston Martin | 3 | Engine | 13 |  |
Question:
how many drivers are from the united states?
Answer:
4