50
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
What is the value of the following expression: $100 - 99 +98 - 97 + 96 - 95 + \cdots + 4 - 3 +2 - 1$?
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
50
What is the value of the following expression: $100 - 99 +98 - 97 + 96 - 95 + \cdots + 4 - 3 +2 - 1$?
train