#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define REP(i, n)           for(int(i)=0;(i)<(n);++(i))

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

    ll maxv = 0;
    for(int i = 1; i < N; i++){
        ll j = N-i;
        maxv = max(maxv, (j + 1)*i + j);
    }
    cout << maxv << endl;

    return 0;
}