#include "bits/stdc++.h"
using namespace std;
#define int long long
#define FOR(i, a, b) for(int i=(a);i<(b);i++)
#define RFOR(i, a, b) for(int i=(b-1);i>=(a);i--)
#define REP(i, n) for(int i=0; i<(n); i++)
#define RREP(i, n) for(int i=(n-1); i>=0; i--)
#define ALL(a) (a).begin(),(a).end()
#define UNIQUE_SORT(l) sort(ALL(l)); l.erase(unique(ALL(l)), l.end());
#define CONTAIN(a, b) find(ALL(a), (b)) != (a).end()
#define array2(type, x, y) array<array<type, y>, x>
#define vector2(type) vector<vector<type> >
#define out(...) printf(__VA_ARGS__)

int dxy[] = {0, 1, 0, -1, 0};

void solve();
signed main()
{
#if DEBUG
    std::ifstream in("input.txt");
    std::cin.rdbuf(in.rdbuf());
#endif
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
    return 0;
}

/*================================*/

int N,M,Q;

int cost(int from, int to) {
    return (from * to) + (to - from);
}

void solve() {
    cin>>N;
    
    int mi = 2;
    int ma = N;
    int s = 1;
    int e = 1;
    int ans = 0;
    
    while(mi <= ma) {
        if (mi == ma) {
            // e -> mi
            ans += cost(e, mi);
            e = mi;
            break;
        }
        if (e > s) {
            // mi -> ma -> s
            ans += cost(mi,ma) + cost(ma,s);
            s = mi;
        } else {
            // e -> ma -> mi
            ans += cost(e,ma) + cost(ma,mi);
            e = mi;
        }
        ma--;
        mi++;
    }
    // e -> s
    if (e != s) ans += cost(e, s);
    
    cout << ans << endl;
}