
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 $\{a_n\}$, where $a_1 = 2$, $a_2 = 3$, and $a_n + a_{n+2} = 2a_{n+1}$ for each $n \geq 1$, calculate the sum $S_{18} = \sum_{k=1}^{18} a_k$.

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