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:
| Name | Took Office | Left Office | President | Party |
| --- | --- | --- | --- | --- |
| Sisavath Keobounphanh | 1996 | 1998 | Nouhak Phoumsavanh | Lao People's Revolutionary Party |
| Oudom Khattigna | 1998 | 1999 | Khamtai Siphandon | Lao People's Revolutionary Party |
| Vacant (1999-2001) | Vacant (1999-2001) | Vacant (1999-2001) | Vacant (1999-2001) | Vacant (1999-2001) |
| Choummaly Sayasone | 2001 | 2006 | Khamtai Siphandon | Lao People's Revolutionary Party |
| Bounnhang Vorachith | 2006 | Incumbent | Choummaly Sayasone | Lao People's Revolutionary Party |
Question:
What is Left Office, when Party is Vacant (1999-2001)?
Answer:
Vacant (1999-2001)