
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 $h(x)$ be a function piecewise defined as \[h(x) = \left\{
\begin{array}{cl}
-x & x\le 0, \\
3x-50 & x>0.
\end{array}
\right.\] If $a$ is negative, find $a$ so that $h(h(h(15)))=h(h(h(a)))$.

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