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. | Rider | Semi-Final Points | Final Points | Final Heats | Total Points |
| --- | --- | --- | --- | --- | --- |
| 1 | Jack Milne | 13 | 15 | (3,3,3,3,3) | 28 |
| 2 | Wilbur Lamoreaux | 12 | 13 | (3,3,3,1,3) | 25 |
| 3 | Cordy Milne | 11 | 12 | (2,3,2,3,2) | 23 |
| 4 | Jack Parker | 11 | 10 | (2,3,1,2,2) | 21 |
| 5 | Ginger Lees | 10 | 9 | (1,1,2,2,3) | 19 |
| 6 | Frank Charles | 10 | 7 | (0,0,1,3,3) | 17 |
| 7 | Lionel Van Praag | 11 | 6 | (3,0,-,3,0) | 17 |
| 8 | Bill Kitchen | 7 | 9 | (1,2,2,2,2) | 16 |
| 9 | George Newton | 11 | 5 | (3,0,0,0,2) | 16 |
| 10 | Eric Langton | 12 | 4 | (1,0,0,3,0) | 16 |
| 11 | Morian Hansen | 7 | 8 | (1,2,3,1,1) | 15 |
| 12 | Eric Chitty | 11 | 4 | (0,2,0,1,1) | 15 |
| 13 | Joe Abbott | 8 | 6 | (2,1,1,2,0) | 14 |
| 14 | Arthur Atkinson | 8 | 6 | (2,0,2,1,1) | 14 |
| 15 | Frank Varey | 8 | 3 | (0,1,1,0,1) | 11 |
| 16 | Tommy Croombs | 6 | 2 | (0,2,0,0,0) | 8 |
| 17 | Bob Harrison | 7 | - | - | 7 |
| 18 | Alec Statham | 6 | 0 | (0) | 6 |
Question:
how many riders were not from the united states?
Answer:
15