HDU 1214（圆桌会议）

#include <iostream>
using namespace std;

int main()
{
	int N;
	int A, B;
	while (cin >> N)
	{
		A = N / 2;
		B = N - A;
		cout << A * (A - 1) / 2 + B * (B - 1) / 2 << endl;
	}
	return 0;
}