Long lasting wars bored country A and B, they decided to dispatch n people to have a peaceful negotiation, respectively. The peaceful negotiation will hold on a round table. But the delegate from country A may has conflict with the delegate from country B. Due to this reason, we hope the people who sit in the round table would not have conflict with the people on both sides. To simplify this problem, suppose the delegate from A exactly has one conflict people in the delegate from B, the delegate from B exactly has one conflict people in the delegate from A. Please calculate probability of the seat choice satisfied the request described above.