
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
In a geometric sequence $\{a_n\}$, $a_1=1$, $a_n > 0$, and the sum of its first $n$ terms is $S_n$. If $a_2$ is the arithmetic mean of $-a_3$ and $a_4$, then the value of $S_6$ is ______.

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