#include using namespace std; typedef long long ll; ll cost(ll x, ll y) { return x * y + x - y; } int main() { cin.tie(0); ios::sync_with_stdio(false); ll N; cin >> N; if (N == 1) { cout << "0\n"; return 0; } ll ans = 0; ll l = 1; ll r = N; for (int i = 0; i < N; i++) { if (i % 2 == 0) { ans += cost(l, r); } else { ans += cost(r, l); } l++; r--; } if (N % 2 == 1) { ans += N - 2; } else { ans += N + N / 2 - 1; } cout << ans << "\n"; return 0; }