
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
Circles $C_1$ and $C_2$ with radii 3 and 9 respectively, are externally tangent and both internally tangent to a circle $C_3$. The centers of the three circles are collinear. A chord of $C_3$, which is a common external tangent of $C_1$ and $C_2$, has its length expressible in the form $\frac{m\sqrt{n}}{p}$, where $m, n, p$ are positive integers, with $m$ and $p$ relatively prime, and $n$ not divisible by the square of any prime. Find the sum $m+n+p$.

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