include

using namespace std;

int main() {

int a, s = 0;
cin >> a;

for (int i = 1; i <= a - 2; i++) {

	for (int j = i + 1; j < a; j++) {

		int k = a - j;

		if (!(j <= k || j - i >= i + k || j - i + k <= i)) {
			s++;
		}
	}
}
cout << s;
return 0;

}