
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
Nathan uses $40^2$ as a base to calculate squares of numbers nearby. He calculates $41^2$ by adding a certain number to $40^2$. Similarly, to determine $39^2$, he subtracts a different number from $40^2$. What number does he subtract to find $39^2$?

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