#include <bits/stdc++.h>
#define rep(i, n) for(long long i = 0; i < n; i++)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
using namespace std;

using lint = long long;
using ld = long double;

int main() {
    lint n;
    cin >> n;
    lint ans = 0;
    for (lint i = 0; i <= n; i++) {
        lint j = n - i;
        ans = max(ans, (i + 1LL) * j + i);
    }
    cout << ans << endl;
}