
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 $s_1, s_2, s_3, s_4$ be the sums of $n$, $3n$, $5n$, and $7n$ terms respectively of the same arithmetic progression with $a$ as the first term and $d$ as the common difference. Express $R' = s_4 - s_3 - s_2$ in terms of $a$, $d$, and $n$.

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