#include <bits/stdc++.h>

using ll =  long long;
#define ld long double
#define rep(i,a,b) for (ll i = a; i < b; i++)
#define irep(i,a,b) for (int i = a; i > b; i--)
#define print(n) cout << n << endl
#define rup(a,b) (a+b-1)/b

using namespace std;

int main(){
    cout << fixed << setprecision(15);
    
    int N;
    cin >> N;
    ll m = 0;
    ll now = 0;
    rep(i,0,N){
        now = (N-i+1)*i + N-i;
        m = max(m,now);
    }
    print(m);
    
    //system("pause");
    return 0;
}