$(1-2)+(3-4)+ \dots +(97-98)+(99-100) = 50(-1) = \boxed{-50}.$
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
Compute: $1-2+3-4+5- \dots +99-100$.
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
-50
Compute: $1-2+3-4+5- \dots +99-100$.
test