PROGRAMMING:Finding the area of a quadrilateral

Find the area of simple quadrilateral ABCD in plane coordinate system. A simple quadrilateral means that the edges only intersect at the vertices.
###Input format:
The integer coordinates of four vertices a, B, C and D are given in turn, and the absolute value of all coordinates is less than 10000.
###Output format:
Output quadrilateral area (retain 1 decimal), title.
###Input example:
Two sets of inputs are given here. For example:
```in
0 0 0 1 1 1 1 0
```
```in
1 2 3 4 5 6 7 8
```
###Output example:
The corresponding output is given here. For example:
```out
one
```
```out
zero
```






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