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;
}