
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
Pedro wrote a list of all positive integers less than 10000 in which each of the digits 1 and 2 appear exactly once. For example, 1234, 231, and 102 were written on the list, but 1102 and 235 are not on the list. How many numbers are there on Pedro's list?

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