
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
Person A digs a water channel. On the first day, they dig $\frac{1}{4}$ of the total length. On the second day, they dig $\frac{5}{21}$ of the remaining length. On the third day, they dig $\frac{1}{2}$ of the remaining length. On the fourth day, they finish the remaining 100 meters. What is the total length of the water channel?

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