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:
| Series | Year | Rank | Average audience share |
| --- | --- | --- | --- |
| 1 | 1992 | Unknown | 14.50m |
| 2 | 1993 | Unknown | Unknown |
| 3 | 1993 | Unknown | Unknown |
| 4 | 1994 | Unknown | Unknown |
| 5 | 1995 | Unknown | Unknown |
| 6 | 1996 | Unknown | 14.60m |
| 7 | 1997–1998 | Unknown | 15.82m |
| 8 | 1998–1999 | 5th | 14.35m |
| 9 | 1999–2000 | 6th | 13.71m |
| 10 | 2000–2001 | 5th | 13.21m |
| 11 | 2001–2002 | 6th | 10.77m |
| 12 | 2002–2003 | 7th | 11.29m |
| 13 | 2003–2004 | 8th | 13.11m |
| 14 | 2004–2005 | 10th | 8.77m |
| 15 | 2005–2006 | 10th | 8.42m |
| 16 | 2006–2007 | 8th | 7.80m |
| 17 | 2007–2008 | 11th | 6.90m |
| 18 | 2008–2010 | 15th | 5.44m (Incl. ITV HD) |
Question:
how many years did heartbeat series run in total?
Answer:
18