
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 26 stamp collectors from different countries who want to exchange the latest commemorative stamps of each country through mutual correspondence. To ensure that each of the 26 individuals ends up possessing a complete set of the latest commemorative stamps from all 26 countries, at least how many letters need to be exchanged?

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