
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 $S_n = 1 + 2 - 3 + 4 + 5 - 6 + \cdots + (-1)^{[(n-1)/3]}n$, where $n = 1, 2, \cdots$. Determine $S_{18} + S_{34} + S_{51}$.
A) 78
B) 79
C) 80
D) 81

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