You are thinking about taking a vacation and taking a tour of Europe. You are currently in Zurich, Switzerland, and your aim is to watch a bullfight in Madrid, Spain, to see the Big Ben in London, U$.$K$.,$ to visit the Colosseum in Rome, Italy, and to drink authentic beers in Berlin, Germany. You decide to borrow a rental helicopter, but you have to pay a high rental fee proportional to the distance traveled. Therefore, after leaving, you wish to return to Zurich again, after visiting the other four cities $($Madrid$,$ London, Rome, Berlin$)$ by traveling a distance as short as possible. Checking the travel distance between cities, as shown in Figure. Now, in what order should you travel so that distance is minimized?