#include <iostream>

int main(void)
{
	unsigned long long N;
	
	std::cin >> N;
	
	unsigned long long a[N];
	unsigned long long a_max = 0;
	
	for(unsigned long long i = 0; i <= N; i ++)	//upper = N
	{
		a[i] = (i + 1) * (N - i + 1);
		
		//for debug
		//std::cout << a[i] << std::endl;
		
		if(a[i] > a_max)
		{
			a_max = a[i];
		}
	}
	
	std::cout << a_max - 1;

	return 0;
}