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:
| Model name | Length | Width | Height | Riders | Capacity | Description | Portable | Notes |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| Skater | 21.5 m (71 ft) | 11.65 m (38.2 ft) | 10.69 m (35.1 ft) | 24 | 600 | Small halfpipe with inwards-facing seats. | Yes |  |
| Disk'O | 24.55 m (80.5 ft) | 9.68 m (31.8 ft) | 10 m (33 ft) | 24 | 600 | Small halfpipe with outwards-facing seats. | Yes |  |
| Surf's Up | 29 m (95 ft) | 11 m (36 ft) | 7.5 m (25 ft) | 20 | 480 | Small halfpipe with hill in middle. Guests stand on rectangular platform. | Yes |  |
| Mega Disk'O | 37.5 m (123 ft) | 10 m (33 ft) | 15.5 m (51 ft) | 24 | 600 | Large halfpipe with outwards-facing seats. | No |  |
| Mega Disk'O | 37.5 m (123 ft) | 10 m (33 ft) | 15.5 m (51 ft) | 40 | 1000 | Large halfpipe with outwards-facing seats. | No |  |
| Skater Coaster | Unknown | Unknown | Unknown | Unknown | Unknown | Large halfpipe with hill in middle. Inwards-facing seats. | Unknown | N/A |
| Disk'O Coaster | 81.5 m (267 ft) | 11.3 m (37 ft) | 15.5 m (51 ft) | 24 | 500 | Large halfpipe with hill in middle. Outwards-facing seats. | No |  |
| Disk'O Coaster | 81.5 m (267 ft) | 11.3 m (37 ft) | 15.5 m (51 ft) | 40 | 600 | Large halfpipe with hill in middle. Outwards-facing seats. | No |  |
Question:
how many riders on the surf's up?
Answer:
20