
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
Consider the sequence of sets of consecutive integers $\{1\}$, $\{2, 3\}$, $\{4, 5, 6\}$, $\{7, 8, 9, 10\}$, $\cdots$, each set containing one more element than its predecessor, with each set starting just after the last element of the previous set. Define $S_n$ as the sum of elements in the nth set. Calculate $S_{15}$.
A) 1645 
B) 1695 
C) 1700 
D) 1750

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