Summary: Starting in Des Moines, use the lines to visit all other cities exactly once, and then return to Des Moines.
 
Story: You have saved up some frequent flier miles with Quad City Air. You now wish to cash in your miles for a dream vacation. Unfortunately the use of your miles is restricted. You must visit each and every city serviced by the airline exactly once. There are fifteen such cities, all located in Iowa, including your home town of Des Moines. Starting in Des Moines, you must visit each of the other fourteen cities exactly once using existing routes, and then return to Des Moines. If you are unable to complete the circuit, you will be stranded in a distant airport, forced to hitchhike home, and charged the full face value of your tickets (equal to two followed by nineteen zeros).
 
Good luck and bon voyage!