
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
Write the numbers $1, 2, 3, \ldots, 1986, 1987$ on the blackboard. Each step involves erasing some of the numbers and writing their sum modulo 7 in their place. After several steps, two numbers remain on the board, one of which is 987. What is the other remaining number?

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