Competitions

# WEEK5 GEOMETRY

# The area of quadrilateral

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

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

The area of a quadrilateral, rounded to integers.

Input example #1

1 4 5 4 4 2 2 1

Output example #1

8