
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
A club has 18 members with varying lengths of membership ranging from 1 to 18 years. The club needs to choose 2 members to be co-presidents on the condition that the two selected members must have at least 5 years difference in their membership length. How many ways can the club choose its co-presidents under this condition?

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