Task: Question Understanding
Input (English): Passage: During 2001, according to several international sources, 28,000–30,000 Pakistani nationals, 14,000–15,000 Afghan Taliban and 2,000–3,000 Al-Qaeda militants were fighting against anti-Taliban forces in Afghanistan as a roughly 45,000 strong military force.  Pakistani President Pervez Musharraf – then as Chief of Army Staff – was responsible for sending thousands of Pakistanis to fight alongside the Taliban and Bin Laden against the forces of Ahmad Shah Massoud. Of the estimated 28,000 Pakistani nationals fighting in Afghanistan, 8,000 were militants recruited in madrassas filling regular Taliban ranks. The document further states that the parents of those Pakistani nationals "know nothing regarding their childs military involvement with the Taliban until their bodies are brought back to Pakistan". A 1998 document by the U.S. State Department confirms that "20–40 percent of [regular] Taliban soldiers are Pakistani."  According to the U.S. State Department report and reports by Human Rights Watch, the other Pakistani nationals fighting in Afghanistan were regular Pakistani soldiers, especially from the Frontier Corps but also from the army providing direct combat support.
Question: When was Pakistani President Pervez Musharraf Chief of Army Staff?
Output (English): date