====== 다각형의 면적 ======

===== 풀이 =====
  * [[ps:이론:다각형#다각형의 넓이]]를 구하는 기본 문제. 구하는 방법은 링크 참고.
  * 시간복잡도는 O(n)

===== 코드 =====
<dkpr py>
"""Solution code for "BOJ 2166. 다각형의 면적".

- Problem link: https://www.acmicpc.net/problem/2166
- Solution link: http://www.teferi.net/ps/problems/boj/2166

Tags: [Math]
"""

import sys
from teflib import geometry


def main():
    N = int(sys.stdin.readline())
    points = [[int(x) for x in sys.stdin.readline().split()] for _ in range(N)]

    area = geometry.twice_of_polygon_area(points) / 2
    print(f'{area:.1f}')


if __name__ == '__main__':
    main()
</dkpr>
  * Dependency: [[:ps:teflib:geometry#twice_of_polygon_area|teflib.geometry.twice_of_polygon_area]]

{{tag>BOJ ps:problems:boj:골드_5}}