Definition: This task involves annotating the answer type to a given question that involve some kind of complex reasoning (including numerical reasoning). Note that the questions require looking at more than one part of the passage to answer. There are 3 possible answer types (i) spans, (ii) numbers and (iii) dates. If the answer can be found in the passage, label it as "span". If the answer is a number, label as "number". Similarly, label "date" if you think the answer to the given question is a date.
Input: Passage: The War on Terror, spanning decades, is a multi-trillion-dollar war. According to the Costs of War Project at Brown University's Watson Institute, the War on Terror will have cost $5.6 trillion for operations between 2001-2018 plus anticipated future costs of veterans' care. According to the Soufan Group in July 2015, the U.S. government was spending $9.4 million per day in operations against ISIS in Syria and Iraq. A March 2011 Congressional report estimated war spending through the fiscal year 2011 at $1.2 trillion, and future spending through 2021 at $1.8 trillion. A June 2011 academic report covering additional areas of war spending estimated it through 2011 at $2.7 trillion, and long-term spending at $5.4 trillion including interest.
Question: How many years has the War on Terror gone on for?
Output:
number