#include<algorithm>
#include<iostream>

typedef long long ll;

ll N;

ll calc( ll k )
{ return k+(N-k)*(k+1); }

int main()
{
	std::cin >> N;
	std::cout << (N&1?std::max(calc(N>>1),calc((N>>1)+1)):calc(N>>1)) << std::endl;

	return 0;
}