# Area of a Polygon

Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

The coordinates of $n$ consecutive points of polygon are given. Find the area of the polygon.

## Input

The number of polygon vertices $n$ is given in the first line. In next $n(3≤n≤50000)$ lines the integer coordinates of consecutive vertices $x_{i},y_{i}(−1000≤x_{i},y_{i}≤1000)$ are given.

## Output

Print the area of the polygon with $3$ decimal digits.

## Examples

Input #1

Answer #1

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