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Area of a Polygon

Statement

 Goal

Given N coordinate pairs, determine the area of the (not necessarily convex) polygon formed by connecting the points in order and connecting the first and last point. The polygon will never self intersect.
Input
Line 1: A positive integer N.
Next N lines: Two integers separated by space, a coordinate pair.
Output
A single integer which is the area of the polygon.
Constraints
2 < N < 21
Example
Input
4
0 0
5 0
5 6
0 6
Output
30

Game modes
Fastest

Test cases
Rectangle Test
Input
4 0 0 5 0 5 6 0 6
Output
30

Validator 1 Validator
Input
4 0 0 6 0 6 6 0 6
Output
36

Weird Test
Input
4 4 10 4 3 11 2 9 7
Output
34

Validator 2 Validator
Input
4 7 8 4 3 11 2 9 7
Output
23

Weirder Test
Input
5 2 4 5 9 3 11 2 10 -2 6
Output
23

Validator 3 Validator
Input
5 2 4 5 11 3 13 2 10 0 9
Output
19

Lots of vertices Test
Input
9 2 0 5 4 3 7 2 10 0 9 1 8 -10 7 -5 5 -3 1
Output
68

Validator 4 Validator
Input
9 2 0 5 4 3 7 2 10 0 9 1 8 -10 7 -5 3 -3 1
Output
75

Solution language

Solution

Stub generator input