
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 \( S = \{1, 2, \ldots, n\} \). Define \( A \) as an arithmetic sequence (with a positive difference) containing at least two terms, where all the terms are elements of \( S \). Moreover, adding any other element from \( S \) to \( A \) must not create a new arithmetic sequence with the same difference as \( A \). Find the number of such sequences \( A \). Note that a sequence with only two terms is also considered an arithmetic sequence.

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