시간 제한 메모리 제한 제출 정답 맞은 사람 정답 비율
1 초 128 MB 963 694 617 76.933%

문제

세 대각선이 한 점에서 만나지 않는 볼록 N각형이 주어졌을 때, 대각선의 교차점의 개수를 세는 프로그램을 작성하시오.

아래 그림은 위의 조건을 만족하는 한 육각형의 교차점 그림이다.

모든 내부각이 180도보다 작은 다각형을 볼록 다각형이라고 한다.

입력

첫째 줄에 N이 주어진다. (3 ≤ N ≤ 100)

출력

첫째 줄에 교차점의 개수를 출력한다.

예제 입력 1

6

예제 출력 1

15
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