
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
On a board, the numbers 1, 2, 3, ..., 19, 20 are written. It is allowed to erase any two numbers \( a \) and \( b \) and write the number \( a + b - 1 \) instead.

What number can remain on the board after 19 such operations?

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