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:
| Date | Tournament | Surface | Opponent | Score |
| --- | --- | --- | --- | --- |
| January 14, 1996 | Auckland , New Zealand | Hard | Brett Steven | 6–4, 6–4 |
| November 1, 1998 | Mexico City , Mexico | Clay | Xavier Malisse | 6–3, 6–3 |
| May 6, 2001 | Munich , Germany | Clay | Antony Dupuis | 6–4, 7–5 |
| July 15, 2001 | Gstaad , Switzerland | Clay | Juan Carlos Ferrero | 6–1, 6–7 (5–7) , 7–5 |
| July 13, 2003 | Gstaad, Switzerland | Clay | Roger Federer | 5–7, 6–3, 6–3, 1–6, 6–3 |
| October 10, 2004 | Tokyo , Japan | Hard | Taylor Dent | 5–7, 6–1, 6–3 |
| November 3, 2004 | Basel , Switzerland | Carpet (i) | David Nalbandian | 5–7, 6–3, 6–4, 1–6, 6–2 |
Question:
What was the surface for the opponent Roger Federer?
Answer:
Clay