Task: Question Understanding
Input (English): Passage: The 1910 Chinese expedition to Tibet or the Chinese invasion of Tibet in 1910 was a military campaign of the Qing dynasty to establish direct rule in Tibet in early 1910. The expedition occupied Lhasa on February 12 and officially deposed the 13th Dalai Lama on the 25th. Qing rule of Tibet was established in the early 18th century after the 1720 Chinese expedition to Tibet, but it was essentially a protectorate rather than a direct rule. The actual rule also waned considerably with the gradual weakening of the Qing dynasty in the 19th century. After the British expedition to Tibet in 1904 and the Sino-British treaty in 1906, the Qing decided to establish direct rule over Tibet and thus sent such an expedition in 1910. As Professor Dawa Norbu stated, "The British military expedition and subsequent convention made the Chinese realize that their power in Tibet had disappeared. So, in 1910 China invaded Tibet, and the Dalai Lama fled to India." In the late winter of 1910, the Manchu government in Beijing was furious with the 13th Dalai Lama. His government, having witnessed the dissolution of its domains in Khams by Qing administrators, and fearing that the amban in Lhasa was going to eliminate its temporal authority, cut this imperial officer off from the sustenance that the Tibet government had guaranteed him in a prior agreement with the Qing court. When a relief column arrived in Lhasa from Sichuan to break the amban out of his isolation, the Dalai Lama fled for British India. However, the direct rule over Tibet proved short-lived: after the outbreak of the Xinhai Revolution and the Xinhai Lhasa turmoil in 1911-1912, Qing rule essentially ended in Lhasa and other parts of Tibet. All Qing forces left Tibet by the end of 1912.
Question: How many years were the Qing forces present in Tibet before leaving?
Output (English): number