You are given an int W.
There is a rectangle in the XY-plane with corners at (0, 0), (0, 1), (W, 0), and (W, 1).
Let T[x] be the triangle with vertices at (0, 1), (W, 1) and (x, 0).
(All points that lie inside the triangle are a part of T[x] as well.)
The objective in this problem is to calculate the area of the region (T xor T xor ... xor T[W]).
(See Notes for a formal definition.)
The figures below show the region (T xor T xor ... xor T[W]) for W=1,2,3,4,5,6.
Return the integer part of the area of the region.