
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Find the maximum value of the following expression: 
\[
\left| \cdots \left| \left| x_1 - x_2 \right| - x_3\right| - \cdots - x_{1990} \right|
\]
where \( x_1, x_2, \cdots, x_{1990} \) are distinct natural numbers from 1 to 1990.

Present the answer in LaTex format: \boxed{Your answer}
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