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Problems

The area of quadrilateral

The area of quadrilateral

Time limit 1 second
Memory limit 64 MiB

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]).

Input data

The coordinates of successive vertices of a quadrilateral are given in a single line. All numbers are integers, not exceeding 100 by absolute value.

Output data

The area of a quadrilateral, rounded to integers.

Examples

Input example #1
1 4 5 4 4 2 2 1
Output example #1
8