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:
| Event | Performance | Athlete | Nation | Place | Date |
| --- | --- | --- | --- | --- | --- |
| 100 m | 9.72 | Usain Bolt | Jamaica | New York City NY, USA | May 31 |
| 100 m | 9.69 | Usain Bolt | Jamaica | Beijing, China | August 16 |
| 200 m | 19.30 | Usain Bolt | Jamaica | Beijing, China | August 20 |
| 4 x 100 m relay | 37.10 | Nesta Carter\nMichael Frater\nUsain Bolt\nAsafa Powell | Jamaica | Beijing, China | August 22 |
| 110 m hurdles | 12.87 | Dayron Robles | Cuba | Ostrava, Czech Republic | June 12 |
| 50 km race walk | 3:34:14 | Denis Nizhegorodov | Russia | Cheboksary, Russia | May 11 |
| Marathon | 2:03:59 | Haile Gebrselassie | Ethiopia | Berlin, Germany | September 28 |
Question:
what is the number of countries listed in the table
Answer:
4