#include <bits/stdc++.h>
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;
}