For an irregular courtyard shaped like a simple polygon, Priya needs its exact area calculated directly from its corner coordinates. Given N vertices of a simple polygon in order (either clockwise or counter-clockwise), print its area using the Shoelace formula, with 2 decimal places.
Input
Line1: N. Next N lines: x y (vertex coordinates in order).
Output
The polygon area, 2 decimals.
Constraints
3 ≤ N ≤ 1000, -10^4 ≤ coords ≤ 10^4
Sample Input
4 0 0 4 0 4 4 0 4
Sample Output
16.00
main.c
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