Question: The 2010–11 Tour de Ski was the 5th edition of the Tour de Ski and took place from 31 December 2010 to which date, Swiss cross-country skier, Dario Cologna won the Men's class?
Related documents: [0]  [DOC] The 2010–11 Tour de Ski was the 5th edition of the Tour de Ski and took place from 31 December 2010 to 9 January 2011. The race started in Oberhof, Germany, and ended in Val di Fiemme, Italy. The defending champions were Lukáš Bauer of the Czech Republic for the men and Poland's Justyna Kowalczyk for the women. Kowalczyk defende her title, and Swiss Dario Cologna won the Men's class. [END] 
[1]  [DOC] Dario Cologna (born 11 March 1986) is a Swiss cross-country skier. He has four overall World Cup victories, three Olympic gold medals, one World Championships gold medal and three Tour de Ski victories in his career so far. [END] 
Answer: 
9 January 2011
9 January 2011