Good day, Codeforces!

Given a polygon with N vertices, where the vertices(x[i], y[i]) are listed in counterclockwise order, you need to check if an angle is concave in the polygon. To better understand what is meant, refer to the provided illustrations:

By (ABC) I will mean the angle where B is the vertex of the angle, and A and C are the sides of the angle.

In that pic, (AFE) and (EDC) are concave angles.

Sorry for my bad English, any help will be appreciated.