
109  ZOJ Monthly, September 2011  I
You want to hold a party. Here's a polygonshaped cake on the table. You'd like to cut the cake into several triangleshaped parts for the invited comers. You have a knife to cut. The trace of each cut is a line segment, whose two endpoints are two vertices of the polygon. Within the polygon, any two cuts ought to be disjoint. Of course, the situation that only the endpoints of two segments intersect is allowed. The cake's considered as a coordinate system. You have known the coordinates of vexteces. Each cut has a cost related to the coordinate of the vertex, whose formula is cost_{i, j} = x_{i} + x_{j} * y_{i} + y_{j} % p. You want to calculate the minimum cost. NOTICE: input assures that NO three adjacent vertices on the polygonshaped cake are in a line. And the cake is not always a convex. InputThere're multiple cases. There's a blank line between two cases. The first line of each case contains two integers, N and p (3 ≤ N, p ≤ 300), indicating the number of vertices. Each line of the following N lines contains two integers, x and y (10000 ≤ x, y ≤ 10000), indicating the coordinate of a vertex. You have known that no two vertices are in the same coordinate. OutputIf the cake is not convex polygonshaped, output "I can't cut.". Otherwise, output the minimum cost. Sample Input3 3 0 0 1 1 0 2 Sample Output0 Author: LI, Zezhou 