Given a list of travel itinerary travel. Each travel[i] contains 3 integers [from, to, fun], which represent where to start, where to end, and how fun it is. An itinerary could start and end at the same spot and could probably have negative fun value.
Each itinerary takes exact 1 day and you have N days of vacation to spend. Each day you can only choose 1 itinerary and get the fun value it has.
At the first day, you can choose any itinerary to start your journey. After that, you can only take the itinerary starting at where you are, so according to your plan, your choices could be limited. If there's no itinerary starting at where you are, your journey ends and you get 0 fun value for the rest of the vacation.
For the given travel and N, return the maximum fun value you can get.