
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
To estimate the number of fish in a pond, 200 fish were caught from the pond and marked, then these fish were released back into the pond. After the marked fish were completely mixed with the rest of the fish, another 100 fish were caught. Among them, 20 fish were marked. Based on this, the estimated number of fish in the pond is ______.

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