
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
There are 21 people lined up, each taking turns to call out a number. The first person calls out 51, and each subsequent person calls out a number that is 5 more than the previous person's number. However, one person made a mistake and instead of adding 5, they subtracted 5. The sum of all the numbers called out is 2021. Identify the person who made the mistake.

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