#include <iostream>
#include <queue>
#include <vector>
#include <cmath>
#include <algorithm>
#include <map>
#include <iomanip>
#include <numeric>

using namespace std;
using ll = long long;
const ll INF = 1e9;
const ll MOD = 1e9 + 7;

int main() {
    int N;
    cin >> N;

    ll mx = 0;
    for (ll upper = 0; upper < N; upper++) {
        mx = max(mx, (N - upper + 1) * upper + (N - upper));
    }

    cout << mx << endl;

    return 0;
}