Give you a simple polygon, please count its area.
Each test case starts with a line containing n (1<= n <= 100000), the number of points. The following n lines of the test case each describe a point, in counter-clockwise order around the hull.
The x- and y-coordinates of each point will be no less than -1000000000 and no greater than 1000000000.
There is a blank between cases.
Output the area of the polygon one decimal places.