3. Between cities A and B, there are three buses: a regular one, which stops in cities V, G, and D (in that order); a fast one, which stops only in city $\Gamma$; and an express, which does not stop anywhere 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 segments 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?
Answer: 17

## Examples of answer notation:

14

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