The area of quadrilateral

Find the area of a quadrilateral with vertices A(x[1],y[1]), B(x[2],y[2]), C(x[3],y[3]), D(x[4],y[4]).

Input

The coordinates of successive vertices of a quadrilateral are given in a single line. All numbers are integers, not exceeding 100 by absolute value.

Output

The area of a quadrilateral, rounded to integers.

Examples