In 1905, the Qing sent Zhao Erfeng to Tibet to retaliate against rebellions. By 1908, Zhao was appointed imperial resident in Lhasa. Zhao was beheaded in December 1911 by pro-Republican forces. The bulk of the area that was historically known as Kham was now claimed to be the Xikang Administrative District, created by the Republican revolutionaries. By the end of 1912, the last Manchu troops were forced out of Tibet through India. Thubten Gyatso, the 13th Dalai Lama, returned to Tibet in January 1913 from Sikkim, where he had been residing. When the new ROC government apologised for the actions of the Qing and offered to restore the Dalai Lama to his former position, he replied that he was not interested in Chinese ranks, that Tibet had never been subordinated to China, that Tibet was an independent country, and that he was assuming the spiritual and political leadership of Tibet. Because of this, many have read this reply as a formal declaration of independence. The Chinese side ignored the response, and Tibet had thirty years free of interference from China.
Question: How many years after Zhao was beheaded were the last Manchu troops forced out of Tibet through India?
Answer: 1