
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
Calculate $2^{1}-1=1$, $2^{2}-1=3$, $2^{3}-1=7$, $2^{4}-1=15$, $2^{5}-1=31$, $\ldots$ Inductively calculate the pattern of the units digit in the results. Guess the units digit of $2^{2015}-1$ is ____.

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