
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
Let $A_{1} A_{2} \cdots A_{21}$ be a regular 21-sided polygon inscribed in a circle. Select $n$ different vertices from $A_{1}, A_{2}, \cdots, A_{21}$ and color them red in such a way that the distances between any two red points are all distinct. Determine the maximum possible value of $n$.

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