P2283 [HNOI2003] Polygon


The first line contains a positive integer $n\ (3 \le n \le 1500)$, denoting the number of vertices of the polygon. Then $n$ lines follow, each containing two integers $x_i,y_i\ (-500 \le x_i,y_i \le 500)$, representing the coordinates of the polygon’s vertices in order.

Output the area of the shaded region, rounded to $2$ decimal places.

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