
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 $f(x) = ax - b$, where $a, b$ are real numbers, $f_1(x) = f(x)$, $f_{n+1}(x) = f(f_n(x))$, for $n=1,2,3,\ldots$. If $f_7(x) = 128x + 381$, then $a+b=$　.

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