eolymp
bolt
Try our new interface for solving problems
Problems

Area of a Polygon

Area of a Polygon

Time limit 1 second
Memory limit 128 MiB

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

Input data

The number of polygon vertices n is given in the first line. In next n~(3 \le n \le 50000) lines the integer coordinates of consecutive vertices x_i, y_i~(-1000 \le x_i, y_i \le 1000) are given.

Output data

Print the area of the polygon with 3 decimal digits.

Examples

Input example #1
3
0 0
0 2
2 0
Output example #1
2.000