The positive integers up to 2007 are alternately subtracted and added:
\[1 - 2 + 3 - 4 + \cdots + 2001 - 2002 + 2003 - 2004 + 2005 - 2006 + 2007.\]What is the value of the expression?
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
The positive integers up to 2007 are alternately subtracted and added:
\[1 - 2 + 3 - 4 + \cdots + 2001 - 2002 + 2003 - 2004 + 2005 - 2006 + 2007.\]What is the value of the expression?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
1004
The positive integers up to 2007 are alternately subtracted and added:
\[1 - 2 + 3 - 4 + \cdots + 2001 - 2002 + 2003 - 2004 + 2005 - 2006 + 2007.\]What is the value of the expression?
train