
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 consecutive numbers written in a row: from 1999 to 2019 inclusive. Vova and Dima, who are fascinated by numerology, performed the following ritual: first, Vova erased several consecutive numbers, then Dima erased several consecutive numbers, and finally, Vova erased several consecutive numbers (in each step, they erased consecutive natural numbers without skipping any gaps that formed). As a result, the sum of the numbers erased by Vova was exactly four times the sum of the numbers erased by Dima, and one number remained in the series. What number remained unerased?

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