Problems
Area of a Polygon
Area of a Polygon
The coordinates of n consecutive points of polygon are given. Find the area of the polygon.
Input data
The number of polygon vertices n is given in the first line. In next n~(3 \le n \le 50000) lines the integer coordinates of consecutive vertices x_i, y_i~(-1000 \le x_i, y_i \le 1000) are given.
Output data
Print the area of the polygon with 3 decimal digits.
Examples
Input example #1
3 0 0 0 2 2 0
Output example #1
2.000