考虑一个拥有 $N$ 个顶点的凸多边形，它满足一个额外的性质：任意三条对角线都不交于同一点。求该多边形中对角线两两相交的交点个数。
下图展示了一个拥有 6 个顶点的此类多边形。
注意：如果一个多边形的所有内角都小于 180 度，则称其为凸多边形。
输入格式
输入只有一行，包含一个整数 $N$（$3 \le N \le 100$）。
输出格式
输出一行一个整数，表示交点的个数。
样例
输入 1
3
输出 1
0
输入 2
4
输出 2
1
输入 3
6
输出 3
15
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총점: 40
#17554. 交点
통계
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