The 2013-14 Tour de Ski was the 8th edition of the Tour de Ski.
 The Stage World Cup event began in Oberhof, Germany on December 28, 2013, and ended in Val di Fiemme, Italy on January 5, 2014.
 The cups are being defended by Justyna Kowalczyk (Poland) and Alexander Legkov (Russia).
 The "last minute changes" introduced by the organizers of 2013-14 edition of Tour de Ski resulted in controversies regarding the balance between the free and classical techniques in the competition.
 Some people, including the four times winner of Tour de Ski and Olympic Champion Justyna Kowalczyk, resigned from participation in protest against changes excessively favoring freestyle competitors.
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.
Gianluca Cologna (born 17 May 1990) is a Swiss cross-country skier.
 His brother Dario Cologna is also a professional cross-country skier.
 He competed in the 2014 Winter Olympics in the Men's team sprint with his brother Dario and finished 5th in the final.
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.
The Tour de Ski (TdS) is a cross-country skiing event held annually since the 2006-2007 season in Central Europe, modeled on the Tour de France of cycling.
 Each Tour de Ski has consisted of six to nine stages, held during late December and early January in the Czech Republic, Germany, Italy, and Switzerland.
 The prize money for the event amount to 1,055,000 Swiss francs (844,000 euros), shared out on both men and women.
 Men's and women's events are held together on the same days, with the only difference being the distance skied.
The 2011–12 Tour de Ski was the 6th edition of the Tour de Ski and took place from 29 December 2011 to 7 January 2012.
 The race started in Oberhof, Germany, and ended in Val di Fiemme, Italy.
 The defending champions were Dario Cologna of Switzerland for the men and Poland's Justyna Kowalczyk (2-time defending champion) for the women.
 Both Cologna and Kowalczyk were able to defend their titles as Tour de Ski champions and became the first athletes ever to win the Tour three times.
The 2008–09 Tour de Ski was the 3rd edition of the Tour de Ski and took place from 27 December 2008 until 4 January 2009.
 The race kicked off in Oberhof, Germany, and finished in Val di Fiemme, Italy.
 The men's event was 102 km, won by Dario Cologna of Switzerland; and the woman's event was 60 km, won by Virpi Kuitunen of Finland.
The 2007–08 Tour de Ski was the 2nd edition of the Tour de Ski and took place from 28 December 2007 until 6 January 2008.
 The race kicked off in Nové Město, the Czech Republic, and finished in Val di Fiemme, Italy, ten days later.
 It featured 8 top international cross-country skiing competitions, of which two were sprint events.
The 2009–10 Tour de Ski was the 4th edition of the Tour de Ski and took place 1–10 January 2010.
 The race started in Oberhof, Germany, and ended in Val di Fiemme, Italy.
 The defending champions are Switzerland's Dario Cologna for the men and Finland's Virpi Kuitunen.
 This year's event was won by Lukáš Bauer of the Czech Republic for the men and Poland's Justyna Kowalczyk for the women.
The 2012-13 Tour de Ski was the 7th edition of the Tour de Ski.
 The event began in Oberhof, Germany on December 29, 2012, and ended in Val di Fiemme, Italy on January 6, 2013.
 The women's cup was won by defending champion Justyna Kowalczyk (Poland) while the men's cup was won by Russian Alexander Legkov ahead of defending champion Dario Cologna of Switzerland.

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?
Answer: 9 January 2011