Problem Description
The managers of a chemical plant, which is notorious for its high pollution, plan to adopt a newly developed device in order to reduce the amount of contaminants emitted. However, engineers in the plant are against this plan, as they doubt the usefulness of the device. As engineers only believe in experimental results, managers decide to hire programmers to make a numerical experiment to convince the engineers.
The new pollution-reducing device consists of several tanks with pipes connecting the tanks. You may assume there is at most one pipe between two tanks. Two tanks are called adjacent if a pipe connects them. When operating, the contaminant circulates in the device among these tanks.
As shown in the Figure-1, the contaminant