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:
| No. | Country | Local title | Format | Start Date | End Date | Episodes | Premiere/Air Dates |
| --- | --- | --- | --- | --- | --- | --- | --- |
| 1.0 | France | Fort Boyard | 1 Team | May 30 | June 3 | 7.0 | 2 July–20 August 2011 |
| 2.0 | Sweden | Fångarna på fortet | Duel | June 6 | June 14 | 12.0 | 23 August–22 October 2011 |
| 3.0 | Norway | Fangene på fortet (The prisoners at the fort) | Duel | June 16 | June 28 | 20.0 | 15–28 August 2011 |
| 4.0 | Algeria | Borj El Abtal (Fort Champions) | 1 Team | June 30 | July 5 | 13.0 | 31 March 2012 |
| 5.0 | France | Prince de LU | Special | July 7 | July 7 | 2.0 | N/A |
| 6.0 | USA and UK | Fort Boyard: Ultimate Challenge | Duel | July 9 | July 15 | 20.0 | 17 October 2011 (USA), 1 January 2012 (UK) |
Question:
What was the production format for the series with the local title Fort Boyard: Ultimate Challenge?
Answer:
Duel