Points symmetry#1451
Given distinct points P_1, P_2, \ldots, P_n on the plane with coordinates (x_i, y_i), where i = 1, \ldots, n. The transformation operates as follows: for every point X_0 on the plane, construct the point X_1 symmetric to X_0 with respect to P_1, then X_2 symmetric to X_1 with respect to P_2, and so on, until X_n symmetric to X_{n-1} with respect to P_n is constructed. If under this transformation there is a unique point that does not change its coordinates (a fixed point), output its coordinates. If there is more than one fixed point, output 0. If there are no fixed points, output -1.
The first line contains the number of points . Each of the next lines contains the integer coordinates of a point (x_i, y_i), where i = 1, \ldots, n. The number of points is between and , inclusive. The coordinates and are integers from to , inclusive.
Output the coordinates of the fixed point if it is unique. If there is more than one fixed point, output 0. If there are no fixed points, output -1.
Example 1