#include <bits/stdc++.h>
using namespace std;

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