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 | Rider | Bike | Laps | Time | Grid | Points |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1 | 21 | Troy Bayliss | Ducati 999 F07 | 22 | 34:11.276 | 1 | 25 |
| 2 | 52 | James Toseland | Honda CBR1000RR | 22 | +2.096 | 2 | 20 |
| 3 | 3 | Max Biaggi | Suzuki GSX-R1000 K7 | 22 | +10.143 | 5 | 16 |
| 4 | 41 | Noriyuki Haga | Yamaha YZF-R1 | 22 | +18.923 | 4 | 13 |
| 5 | 11 | Troy Corser | Yamaha YZF-R1 | 22 | +19.742 | 3 | 11 |
| 6 | 57 | Lorenzo Lanzi | Ducati 999 F07 | 22 | +24.765 | 10 | 10 |
| 7 | 111 | Ruben Xaus | Ducati 999 F06 | 22 | +27.404 | 8 | 9 |
| 8 | 76 | Max Neukirchner | Suzuki GSX-R1000 K6 | 22 | +34.614 | 7 | 8 |
| 9 | 10 | Fonsi Nieto | Kawasaki ZX-10R | 22 | +35.339 | 6 | 7 |
| 10 | 99 | Steve Martin | Honda CBR1000RR | 22 | +36.238 | 11 | 6 |
| 11 | 44 | Roberto Rolfo | Honda CBR1000RR | 22 | +38.067 | 15 | 5 |
| 12 | 25 | Josh Brookes | Honda CBR1000RR | 22 | +47.078 | 12 | 4 |
| 13 | 38 | Shinichi Nakatomi | Yamaha YZF-R1 | 22 | +58.571 | 17 | 3 |
| 14 | 96 | Jakub Smrž | Ducati 999 F05 | 22 | +1:08.000 | 14 | 2 |
| 15 | 53 | Alex Polita | Suzuki GSX-R1000 K6 | 22 | +1:22.584 | 18 | 1 |
| 16 | 73 | Christian Zaiser | MV Agusta F4 1000R | 22 | +1:28.374 | 19 |  |
| 17 | 42 | Dean Ellison | Ducati 999RS | 22 | +1:30.184 | 21 |  |
| 18 | 36 | Jiri Drazdak | Yamaha YZF-R1 | 21 | +1 Lap | 20 |  |
| Ret | 55 | Régis Laconi | Kawasaki ZX-10R | 16 | Retirement | 9 |  |
| Ret | 84 | Michel Fabrizio | Honda CBR1000RR | 5 | Retirement | 13 |  |
Question:
what is the number of non-retired riders?
Answer:
18