#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

ll f(ll L) {
	return L * L - L * (L+1) / 2;
}
int main() {
	ll L; cin >> L;
	ll a = L = (L + 1) / 2;
	ll b = a-1;
	cout << f(a)+f(b) << endl;
}