The area of quadrilateral#946
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).
The coordinates of the successive vertices of the quadrilateral are given in a single line: x_1 y_1 x_2 y_2 x_3 y_3 x_4 y_4. All input values are integers and satisfy |x_i| \le 100, |y_i| \le 100 for i = 1..4.
Output the area of the quadrilateral, rounded to the nearest integer.
Example 1