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:
| Outcome | Date | Surface | Opponent in the final | Score in the final |
| --- | --- | --- | --- | --- |
| Runner-up | 17 August 2008 | Hard | Juan Martín del Potro | 3–6, 3–6 |
| Runner-up | 4 October 2009 | Hard (i) | Gilles Simon | 5–7, 3–6 |
| Winner | 24 October 2010 | Hard (i) | Marcos Baghdatis | 3–6, 6–4, 6–3 |
| Runner-up | 15 January 2011 | Hard | Gilles Simon | 5–7, 6–7 (4–7) |
| Runner-up | 23 October 2011 | Hard (i) | Janko Tipsarević | 4–6, 2–6 |
Question:
What was the surface on 23 October 2011?
Answer:
Hard (i)