
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
Given a sequence of numbers $a_1$, $a_2$, $a_3$, …, $a_n$, …, where $a_1=0$, $a_2=2a_1+1$, $a_3=2a_2+1$, …, $a_{n+1}=2a_n+1$, …, calculate the units digit of $a_{2004}-a_{2003}$.

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