
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
Given a sequence: 2008, 2009, 1, -2008, -2009, … starting from the second term, each term equals the sum of the term before and the term after it. The sum of the first 2009 terms of this sequence $S_{2009}$ equals ____.

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