
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 three buses that travel between cities A and B: a regular bus that stops in cities C, D, and E (in that order); a high-speed bus that only stops in city \( \Gamma \); and an express bus that does not stop along the way.

All buses travel on different roads, at a constant speed, and take an integer number of hours to travel between any two stops. The road sections between stops are straight.

The regular bus travels from A to B in 20 hours (excluding the time spent at stops). What is the maximum time (in hours) that the express bus can take to travel from A to B?

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